├── .gitignore ├── .idea ├── compiler.xml ├── misc.xml ├── modules.xml ├── solutions.md ├── vcs.xml └── wrap-up-notes.md ├── LICENSE ├── README.md ├── lib ├── hamcrest-core-1.3-javadoc.jar ├── hamcrest-core-1.3.jar ├── junit-4.13.1-javadoc.jar └── junit-4.13.1.jar ├── refactoring-golf.iml └── src └── payroll ├── hole01 ├── Payslip.java ├── PayslipTest.java └── notes.md ├── hole02 ├── Payslip.java ├── PayslipTest.java └── notes.md ├── hole03 ├── Payslip.java ├── PayslipTest.java └── notes.md ├── hole04 ├── Payslip.java ├── PayslipTest.java ├── TaxCalculator.java └── notes.md ├── hole05 ├── Payslip.java ├── PayslipTest.java ├── TaxCalculator.java └── notes.md ├── hole06 ├── Payslip.java ├── PayslipTest.java ├── TaxCalculator.java └── notes.md ├── hole07 ├── Payslip.java ├── PayslipTest.java ├── TaxCalculator.java └── notes.md ├── hole08 ├── Payslip.java ├── PayslipTest.java ├── TaxCalculator.java └── notes.md ├── hole09 ├── BandedTaxCalculator.java ├── BandedTaxCalculatorTest.java ├── Payslip.java ├── PayslipTaxTest.java ├── PayslipTest.java ├── TaxCalculator.java └── notes.md └── hole10 ├── BandedTaxCalculator.java ├── NullTaxCalculator.java ├── Payslip.java ├── PayslipTaxTest.java ├── PayslipTest.java └── TaxCalculator.java /.gitignore: -------------------------------------------------------------------------------- 1 | # Compiled class file 2 | *.class 3 | 4 | # Log file 5 | *.log 6 | 7 | # BlueJ files 8 | *.ctxt 9 | 10 | # Mobile Tools for Java (J2ME) 11 | .mtj.tmp/ 12 | 13 | # Package Files # 14 | *.jar 15 | *.war 16 | *.nar 17 | *.ear 18 | *.zip 19 | *.tar.gz 20 | *.rar 21 | 22 | # virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml 23 | hs_err_pid* 24 | /out/ 25 | /.idea/workspace.xml 26 | -------------------------------------------------------------------------------- /.idea/compiler.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | -------------------------------------------------------------------------------- /.idea/misc.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | 5 | 6 | -------------------------------------------------------------------------------- /.idea/modules.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | -------------------------------------------------------------------------------- /.idea/solutions.md: -------------------------------------------------------------------------------- 1 | Refactoring 1 2 | - rename 6 variables. 6 points. 3 | 4 | Refactoring 2 5 | - extract local variable tax 6 | - extract method calculatedTax() 7 | - inline local variable tax in getNet() 8 | 9 | Refactoring 3 10 | - extract MethodObject to create TaxCalculator 11 | - inline generate invoke() method 12 | - in calculatedTax, IntroduceParameter grossSalary 13 | - convert TaxCalculator() to field, initialised in Constructor 14 | - make TaxCalculator static 15 | - introduce taxCalculator parameter to constructor 16 | - rename calculatedTax to taxFor 17 | - change scope of taxFor to public 18 | - move TaxCalculator to top level 19 | 20 | Refactoring 4 21 | - extract method assertNetForGross 22 | - introduce parameter netSalary 23 | - fix tests manually 24 | - move assertNetForGross to bottom 25 | 26 | Refactoring 5 27 | - Extract variable for tax bracket rates (x3) 28 | - extract variable for tax bracket starts (x3) 29 | - extract remaining gross for middle and lower brackets (x2) 30 | - extract grossToTaxInBandsBelowCurrent() (IDE promts for a duplicate) 31 | - extract taxInBand() (IDE prompts for 2 duplicates) 32 | - rename parameter to grossSalaryExcludingPartAlreadyTaxedAtHigherRate 33 | - extract grossToTaxInBand 34 | - inline upperTaxBracketGross 35 | 36 | Refactoring 6 37 | - Extract ParameterObject with bracketMinimumGross and taxRate 38 | - change signature to add taxBand parameter to getGrossToTaxInBand 39 | - reference bracketMinimumGross from taxBand 40 | - remove unused parameter 41 | - move getGrossToTaxInBand to TaxBand 42 | - extract variables for TaxBands 43 | - add TaxBand parameter to getGrossToTaxInBandsBelowCurrent 44 | - use bracketMinimumGross from taxBand parameter 45 | - remove unused bracketMinimumGross 46 | - move getGrossToTaxInBandsBelowCurrent to TaxBand 47 | - remove unused getBracketMinimumGross 48 | - move getTaxInBand to TaxBand 49 | - inline getTaxRate 50 | - inline tax band constants 51 | 52 | Refactoring 07 53 | - order lower/middle/upper tax bands 54 | - Add middleTaxBand to upperTaxBandConstructor (1 x2) 55 | - Create constructor (Default null, use any var) 56 | - Assign to field 57 | - extract taxForLowerBands(lower, middle) 58 | - move taxForLowerBands to middleTaxBand 59 | - use this.lowerTaxBand instead of parameter 60 | - remove unused parameter 61 | - rename remainingGrossForMiddleAndLowerBrackets to grossSalary 62 | - rename grossToTaxInBandsBelowCurrent to grossToTaxAtLowerBand 63 | - rename grossToTaxInBand to grossInBand 64 | - rename grossSalaryExcludingPartAlreadyTaxedAtHigherRate to grossSalary 65 | - rename taxInBand to taxForBand 66 | - rename grossSalaryExcludingPartAlreadyTaxedAtHigherRate to grossSalary 67 | - extract variable lowerMiddleTax 68 | - extract method taxFor (lowerMiddleTax) 69 | - move taxFor to TaxBand 70 | - rename remainingGrossForMiddleAndLowerBrackets to grossSalary 71 | - inline low and middle bracket tax (x2) 72 | - inline remainingGrossForLowerBracket 73 | - replace taxForBand with taxFor within taxForLowerBands (failing test) 2x2 74 | - null check (2) 75 | - replace body of TaxCalculator.taxFor with upperTaxBand.taxFor() 76 | 77 | Refactoring 08 78 | - extract TaxCalculator as interface (TaxCalculatorTemp) 79 | - make TaxBand.taxFor public 80 | - move TaxBand up to top level and rename to BandedTaxCalculator 81 | - rename lowerTaxBand to lowerBandCalculator 82 | - implement TaxCalculator (2) 83 | - move calculators from TaxCalculatorTemp to test 84 | - delete TaxCalculatorTemp 85 | -------------------------------------------------------------------------------- /.idea/vcs.xml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | 5 | 6 | -------------------------------------------------------------------------------- /.idea/wrap-up-notes.md: -------------------------------------------------------------------------------- 1 | # Lessons 2 | - modern IDEs can do more than you expect 3 | - thinking at a higher level (e.g. "extract method" rather than a series of text edits) 4 | - undo and history also works at a structural level 5 | - the development environment becomes, in effect, part of the language. 6 | This goes back to Lisp and Smalltalk 7 | - it's frustratingly not perfect 8 | - sometimes it's magical 9 | - sometimes it getting there can be indirect 10 | - Defactoring is a thing 11 | 12 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Refactoring Golf 2 | `https://github.com/sf105/refactoring-golf` 3 | 4 | _Refactoring Golf_ is a game designed to stretch your refactoring muscles and 5 | to get you to explore your IDE to see what's really possible using 6 | shortcuts and automation. The idea is to focus on one aspect of coding 7 | and see how far it can be pushed. 8 | 9 | This repository contains multiple versions of a simple class to calculate tax on a payslip. 10 | 11 | * The first 5,000 is tax free 12 | * Up to 20,000 is taxed at 10% 13 | * Up to 40,000 is taxed at 20% 14 | * Above 40,000 is taxed at 40% 15 | 16 | Each version is a refactoring of the previous version. Sticking with the golf metaphor, 17 | each version is called a "hole". 18 | 19 | Your goal is to refactor from each _hole_ to the next safely and efficiently, 20 | using the features of the IDE with as few "strokes" as possible, where a _stroke_ is 21 | an action that changes the code. Every stroke costs you points. 22 | 23 | Your pairing partner should carefully score you as follows: 24 | 25 | - 0 points for formatting and selection 26 | - 1 point for every change made to the code using a shortcut or automated IDE feature 27 | (e.g., an automated refactoring, code template, rename, or Find/Replace) 28 | - 2 points for every manual edit. Note that a single "edit" could cover multiple lines of code. 29 | - There is a _double points_ penalty for changes that leave the code failing the tests or not compiling. 30 | 31 | Allow yourselves a maximum of 2 attempts at each round to determine your best score. 32 | 33 | ## Hints 34 | - Each version has a `notes.md` file that describes the motivation for the next refactoring. 35 | - You might want to keep the target code open in another window, or perhaps on the partner's machine. 36 | It's easy to get confused about which file is which. 37 | - Commit your code frequently, especially after each refactoring stage. That will make rolling-back easier 38 | if you want to make another attempt or if you get confused. 39 | - Run the tests after each "stroke". You can do this by selecting the top-level *refactoring-golf* in 40 | the project view and selecting `Run 'All Tests'` from the pop-up menu. 41 | - Check your code in frequently so it's easier to try a refactoring more than once. Idea also has 42 | an excellent _Local History_ option. 43 | - Also look at the options available from `Show Context Action` if you right-click on a feature. The (very useful) keyboard shortcut varies by platform. 44 | 45 | ## Practical 46 | - This exercise was written with _Intellj Idea_. You should be able to clone the repository 47 | and _Open_ it as a project. 48 | - You might have to set the JDK for the project. The project will build with versions from Java 11. 49 | - Idea has a _Keymap Reference_ available from the help menu. If you're unfamiliar, it's worth reading this through 50 | and keeping it handy 51 | - Mouse actions are fine to start with, but learn the key shortcuts 52 | 53 | ## Example scores 54 | These are some example scores, achieved using IntelliJ. 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 |
HoleBest scoreNotes
1 6
2 3
3 9
4 17 lots of manual edits
5 13
6 14
7 29 This one is quite hard, but is possible
8 8
9 xx
68 | 69 | ## Alternative version 70 | There's an alternative version that was implemented using TDD from scratch in the 71 | `reimplemented-with-tdd` branch of the repository. 72 | 73 | ## Acknowledgements 74 | This exercise was mainly taken from an example by Lance Walton. 75 | 76 | Other ideas were taken from David Denton and Ivan Sanchez, inspired by @ivanmoore and @rchatley 77 | 78 | These instructions were mostly stolen from @jasongorman's 79 | Refactoring Golf. 80 | 81 | ## Notes 82 | 83 | - we used `long` for the calculations, like the alternative TDD version. Both should probably 84 | use a decimal format. 85 | -------------------------------------------------------------------------------- /lib/hamcrest-core-1.3-javadoc.jar: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/sf105/refactoring-golf/5dd0014ee2b37da6220a0b87fa0d01943b72b63f/lib/hamcrest-core-1.3-javadoc.jar -------------------------------------------------------------------------------- /lib/hamcrest-core-1.3.jar: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/sf105/refactoring-golf/5dd0014ee2b37da6220a0b87fa0d01943b72b63f/lib/hamcrest-core-1.3.jar -------------------------------------------------------------------------------- /lib/junit-4.13.1-javadoc.jar: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/sf105/refactoring-golf/5dd0014ee2b37da6220a0b87fa0d01943b72b63f/lib/junit-4.13.1-javadoc.jar -------------------------------------------------------------------------------- /lib/junit-4.13.1.jar: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/sf105/refactoring-golf/5dd0014ee2b37da6220a0b87fa0d01943b72b63f/lib/junit-4.13.1.jar -------------------------------------------------------------------------------- /refactoring-golf.iml: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | -------------------------------------------------------------------------------- /src/payroll/hole01/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole01; 2 | 3 | public class Payslip { 4 | private final long sal; 5 | 6 | public Payslip(final long slry) { 7 | this.sal = slry; 8 | } 9 | 10 | public long getNet() { 11 | final long ltbg = Math.max(Math.min(sal, 20000) - 5000, 0); 12 | final long mtbg = Math.max(Math.min(sal, 40000) - 20000, 0); 13 | final long utbg = Math.max(sal - 40000, 0); 14 | return Math.round(sal - (ltbg * 0.1 + mtbg * 0.2 + utbg * 0.4)); 15 | } 16 | } 17 | -------------------------------------------------------------------------------- /src/payroll/hole01/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole01; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | Payslip payslip = new Payslip(5000); 11 | assertEquals(5000, payslip.getNet()); 12 | } 13 | 14 | @Test 15 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 16 | final Payslip payslip = new Payslip(10000); 17 | assertEquals(9500, payslip.getNet()); 18 | 19 | final Payslip payslip2 = new Payslip(20000); 20 | assertEquals(18500, payslip2.getNet()); 21 | } 22 | 23 | @Test 24 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 25 | final Payslip payslip = new Payslip(25000); 26 | assertEquals(22500, payslip.getNet()); 27 | 28 | final Payslip payslip2 = new Payslip(40000); 29 | assertEquals(34500, payslip2.getNet()); 30 | } 31 | 32 | @Test 33 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 34 | final Payslip payslip = new Payslip(50000); 35 | assertEquals(40500, payslip.getNet()); 36 | 37 | final Payslip payslip2 = new Payslip(60000); 38 | assertEquals(46500, payslip2.getNet()); 39 | } 40 | } 41 | -------------------------------------------------------------------------------- /src/payroll/hole01/notes.md: -------------------------------------------------------------------------------- 1 | This is a simple tax calculation, but the variable names need to be readable. 2 | -------------------------------------------------------------------------------- /src/payroll/hole02/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole02; 2 | 3 | public class Payslip { 4 | private final long grossSalary; 5 | 6 | public Payslip(final long grossSalary) { 7 | this.grossSalary = grossSalary; 8 | } 9 | 10 | public long getNet() { 11 | final long lowerTaxBracketGross = Math.max(Math.min(grossSalary, 20000) - 5000, 0); 12 | final long middleTaxBracketGross = Math.max(Math.min(grossSalary, 40000) - 20000, 0); 13 | final long upperTaxBracketGross = Math.max(grossSalary - 40000, 0); 14 | return Math.round(grossSalary - (lowerTaxBracketGross * 0.1 + middleTaxBracketGross * 0.2 + upperTaxBracketGross * 0.4)); 15 | } 16 | } 17 | -------------------------------------------------------------------------------- /src/payroll/hole02/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole02; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | Payslip payslip = new Payslip(5000); 11 | assertEquals(5000, payslip.getNet()); 12 | } 13 | 14 | @Test 15 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 16 | final Payslip payslip = new Payslip(10000); 17 | assertEquals(9500, payslip.getNet()); 18 | 19 | final Payslip payslip2 = new Payslip(20000); 20 | assertEquals(18500, payslip2.getNet()); 21 | } 22 | 23 | @Test 24 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 25 | final Payslip payslip = new Payslip(25000); 26 | assertEquals(22500, payslip.getNet()); 27 | 28 | final Payslip payslip2 = new Payslip(40000); 29 | assertEquals(34500, payslip2.getNet()); 30 | } 31 | 32 | @Test 33 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 34 | final Payslip payslip = new Payslip(50000); 35 | assertEquals(40500, payslip.getNet()); 36 | 37 | final Payslip payslip2 = new Payslip(60000); 38 | assertEquals(46500, payslip2.getNet()); 39 | } 40 | } 41 | -------------------------------------------------------------------------------- /src/payroll/hole02/notes.md: -------------------------------------------------------------------------------- 1 | `Payslip.getNet()` mixes up both the calculation of the tax and subtraction from the gross pay. 2 | This should be split out 3 | -------------------------------------------------------------------------------- /src/payroll/hole03/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole03; 2 | 3 | public class Payslip { 4 | private final long grossSalary; 5 | 6 | public Payslip(final long grossSalary) { 7 | this.grossSalary = grossSalary; 8 | } 9 | 10 | public long getNet() { 11 | return grossSalary - calculatedTax(); 12 | } 13 | 14 | private long calculatedTax() { 15 | final long lowerTaxBracketGross = Math.max(Math.min(grossSalary, 20000) - 5000, 0); 16 | final long middleTaxBracketGross = Math.max(Math.min(grossSalary, 40000) - 20000, 0); 17 | final long upperTaxBracketGross = Math.max(grossSalary - 40000, 0); 18 | return Math.round(lowerTaxBracketGross * 0.1 + middleTaxBracketGross * 0.2 + upperTaxBracketGross * 0.4); 19 | } 20 | } 21 | -------------------------------------------------------------------------------- /src/payroll/hole03/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole03; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | Payslip payslip = new Payslip(5000); 11 | assertEquals(5000, payslip.getNet()); 12 | } 13 | 14 | @Test 15 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 16 | final Payslip payslip = new Payslip(10000); 17 | assertEquals(9500, payslip.getNet()); 18 | 19 | final Payslip payslip2 = new Payslip(20000); 20 | assertEquals(18500, payslip2.getNet()); 21 | } 22 | 23 | @Test 24 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 25 | final Payslip payslip = new Payslip(25000); 26 | assertEquals(22500, payslip.getNet()); 27 | 28 | final Payslip payslip2 = new Payslip(40000); 29 | assertEquals(34500, payslip2.getNet()); 30 | } 31 | 32 | @Test 33 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 34 | final Payslip payslip = new Payslip(50000); 35 | assertEquals(40500, payslip.getNet()); 36 | 37 | final Payslip payslip2 = new Payslip(60000); 38 | assertEquals(46500, payslip2.getNet()); 39 | } 40 | } 41 | -------------------------------------------------------------------------------- /src/payroll/hole03/notes.md: -------------------------------------------------------------------------------- 1 | `Payslip` knows too much about tax calculations 2 | -------------------------------------------------------------------------------- /src/payroll/hole04/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole04; 2 | 3 | public class Payslip { 4 | private final long grossSalary; 5 | private final TaxCalculator taxCalculator; 6 | 7 | public Payslip(final long grossSalary, final TaxCalculator taxCalculator) { 8 | this.grossSalary = grossSalary; 9 | this.taxCalculator = taxCalculator; 10 | } 11 | 12 | public long getNet() { 13 | return grossSalary - taxCalculator.taxFor(grossSalary); 14 | } 15 | } 16 | -------------------------------------------------------------------------------- /src/payroll/hole04/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole04; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | Payslip payslip = new Payslip(5000, new TaxCalculator()); 11 | assertEquals(5000, payslip.getNet()); 12 | } 13 | 14 | @Test 15 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 16 | final Payslip payslip = new Payslip(10000, new TaxCalculator()); 17 | assertEquals(9500, payslip.getNet()); 18 | 19 | final Payslip payslip2 = new Payslip(20000, new TaxCalculator()); 20 | assertEquals(18500, payslip2.getNet()); 21 | } 22 | 23 | @Test 24 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 25 | final Payslip payslip = new Payslip(25000, new TaxCalculator()); 26 | assertEquals(22500, payslip.getNet()); 27 | 28 | final Payslip payslip2 = new Payslip(40000, new TaxCalculator()); 29 | assertEquals(34500, payslip2.getNet()); 30 | } 31 | 32 | @Test 33 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 34 | final Payslip payslip = new Payslip(50000, new TaxCalculator()); 35 | assertEquals(40500, payslip.getNet()); 36 | 37 | final Payslip payslip2 = new Payslip(60000, new TaxCalculator()); 38 | assertEquals(46500, payslip2.getNet()); 39 | } 40 | } 41 | -------------------------------------------------------------------------------- /src/payroll/hole04/TaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole04; 2 | 3 | public class TaxCalculator { 4 | public long taxFor(final long grossSalary) { 5 | final long lowerTaxBracketGross = Math.max(Math.min(grossSalary, 20000) - 5000, 0); 6 | final long middleTaxBracketGross = Math.max(Math.min(grossSalary, 40000) - 20000, 0); 7 | final long upperTaxBracketGross = Math.max(grossSalary - 40000, 0); 8 | return Math.round(lowerTaxBracketGross * 0.1 + middleTaxBracketGross * 0.2 + upperTaxBracketGross * 0.4); 9 | } 10 | } 11 | -------------------------------------------------------------------------------- /src/payroll/hole04/notes.md: -------------------------------------------------------------------------------- 1 | There's lots of duplication in the tests 2 | -------------------------------------------------------------------------------- /src/payroll/hole05/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole05; 2 | 3 | public class Payslip { 4 | private final long grossSalary; 5 | private final TaxCalculator taxCalculator; 6 | 7 | public Payslip(final long grossSalary, final TaxCalculator taxCalculator) { 8 | this.grossSalary = grossSalary; 9 | this.taxCalculator = taxCalculator; 10 | } 11 | 12 | public long getNet() { 13 | return grossSalary - taxCalculator.taxFor(grossSalary); 14 | } 15 | } 16 | -------------------------------------------------------------------------------- /src/payroll/hole05/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole05; 2 | 3 | import static org.junit.Assert.assertEquals; 4 | 5 | import org.junit.Test; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | assertNetGivenGross(5000, 5000); 11 | } 12 | 13 | @Test 14 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 15 | assertNetGivenGross(10000, 9500); 16 | assertNetGivenGross(20000, 18500); 17 | } 18 | 19 | @Test 20 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 21 | assertNetGivenGross(25000, 22500); 22 | assertNetGivenGross(40000, 34500); 23 | } 24 | 25 | @Test 26 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 27 | assertNetGivenGross(50000, 40500); 28 | assertNetGivenGross(60000, 46500); 29 | } 30 | 31 | private void assertNetGivenGross(final int gross, final int expectedNet) { 32 | final Payslip payslip = new Payslip(gross, new TaxCalculator()); 33 | assertEquals(expectedNet, payslip.getNet()); 34 | } 35 | } 36 | -------------------------------------------------------------------------------- /src/payroll/hole05/TaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole05; 2 | 3 | public class TaxCalculator { 4 | public long taxFor(final long grossSalary) { 5 | final long lowerTaxBracketGross = Math.max(Math.min(grossSalary, 20000) - 5000, 0); 6 | final long middleTaxBracketGross = Math.max(Math.min(grossSalary, 40000) - 20000, 0); 7 | final long upperTaxBracketGross = Math.max(grossSalary - 40000, 0); 8 | return Math.round(lowerTaxBracketGross * 0.1 + middleTaxBracketGross * 0.2 + upperTaxBracketGross * 0.4); 9 | } 10 | } 11 | -------------------------------------------------------------------------------- /src/payroll/hole05/notes.md: -------------------------------------------------------------------------------- 1 | The `TaxCalculator` code does not represent the domain well, 2 | which has different tax rates for different bands of income. 3 | -------------------------------------------------------------------------------- /src/payroll/hole06/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole06; 2 | 3 | public class Payslip { 4 | private final long grossSalary; 5 | private final TaxCalculator taxCalculator; 6 | 7 | public Payslip(final long grossSalary, final TaxCalculator taxCalculator) { 8 | this.grossSalary = grossSalary; 9 | this.taxCalculator = taxCalculator; 10 | } 11 | 12 | public long getNet() { 13 | return grossSalary - taxCalculator.taxFor(grossSalary); 14 | } 15 | } 16 | -------------------------------------------------------------------------------- /src/payroll/hole06/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole06; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | assertNetForGross(5000, 5000); 11 | } 12 | 13 | @Test 14 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 15 | assertNetForGross(10000, 9500); 16 | assertNetForGross(20000, 18500); 17 | } 18 | 19 | @Test 20 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 21 | assertNetForGross(25000, 22500); 22 | assertNetForGross(40000, 34500); 23 | } 24 | 25 | @Test 26 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 27 | assertNetForGross(50000, 40500); 28 | assertNetForGross(60000, 46500); 29 | } 30 | 31 | private void assertNetForGross(final int gross, final int expectedNet) { 32 | final Payslip payslip = new Payslip(gross, new TaxCalculator()); 33 | assertEquals(expectedNet, payslip.getNet()); 34 | } 35 | } 36 | -------------------------------------------------------------------------------- /src/payroll/hole06/TaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole06; 2 | 3 | public class TaxCalculator { 4 | public long taxFor(final long grossSalary) { 5 | final long upperTaxBracketStart = 40000; 6 | final double upperTaxBracketRate = 0.4; 7 | final long upperTaxBracketTax = taxInBand(grossSalary, upperTaxBracketStart, upperTaxBracketRate); 8 | final long remainingGrossForMiddleAndLowerBrackets = grossToTaxInBandsBelowCurrent(grossSalary, upperTaxBracketStart); 9 | 10 | final long middleTaxBracketStart = 20000; 11 | final double middleTaxBracketRate = 0.2; 12 | final long middleTaxBracketTax = taxInBand(remainingGrossForMiddleAndLowerBrackets, middleTaxBracketStart, middleTaxBracketRate); 13 | final long remainingGrossForLowerBracket = grossToTaxInBandsBelowCurrent(remainingGrossForMiddleAndLowerBrackets, middleTaxBracketStart); 14 | 15 | final long lowerTaxBracketStart = 5000; 16 | final double lowerTaxBracketRate = 0.1; 17 | final long lowerTaxBracketTax = taxInBand(remainingGrossForLowerBracket, lowerTaxBracketStart, lowerTaxBracketRate); 18 | 19 | return lowerTaxBracketTax + middleTaxBracketTax + upperTaxBracketTax; 20 | } 21 | 22 | private long taxInBand(final long grossSalaryExcludingPartAlreadyTaxedAtHigherRate, final long bracketMinimumGross, final double taxRate) { 23 | return Math.round(grossToTaxInBand(grossSalaryExcludingPartAlreadyTaxedAtHigherRate, bracketMinimumGross) * taxRate); 24 | } 25 | 26 | private long grossToTaxInBandsBelowCurrent(final long grossSalary, final long bracketMinimumGross) { 27 | return Math.min(grossSalary, bracketMinimumGross); 28 | } 29 | 30 | private long grossToTaxInBand(long grossSalaryExcludingPartAlreadyTaxedAtHigherRate, final long bracketMinimumGross) { 31 | return Math.max(0, grossSalaryExcludingPartAlreadyTaxedAtHigherRate - bracketMinimumGross); 32 | } 33 | } 34 | -------------------------------------------------------------------------------- /src/payroll/hole06/notes.md: -------------------------------------------------------------------------------- 1 | `TaxCalculator` is very hard-coded 2 | There appears to be a common pattern around the start of each tax bracket and 3 | the rate for that bracket, both of which are likely to change. 4 | Introduce a structure to represent that concept. 5 | -------------------------------------------------------------------------------- /src/payroll/hole07/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole07; 2 | 3 | public class Payslip { 4 | private final long grossSalary; 5 | private final TaxCalculator taxCalculator; 6 | 7 | public Payslip(final long grossSalary, final TaxCalculator taxCalculator) { 8 | this.grossSalary = grossSalary; 9 | this.taxCalculator = taxCalculator; 10 | } 11 | 12 | public long getNet() { 13 | return grossSalary - taxCalculator.taxFor(grossSalary); 14 | } 15 | } 16 | -------------------------------------------------------------------------------- /src/payroll/hole07/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole07; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | assertNetForGross(5000, 5000); 11 | } 12 | 13 | @Test 14 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 15 | assertNetForGross(10000, 9500); 16 | assertNetForGross(20000, 18500); 17 | } 18 | 19 | @Test 20 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 21 | assertNetForGross(25000, 22500); 22 | assertNetForGross(40000, 34500); 23 | } 24 | 25 | @Test 26 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 27 | assertNetForGross(50000, 40500); 28 | assertNetForGross(60000, 46500); 29 | } 30 | 31 | private void assertNetForGross(final int gross, final int expectedNet) { 32 | final Payslip payslip = new Payslip(gross, new TaxCalculator()); 33 | assertEquals(expectedNet, payslip.getNet()); 34 | } 35 | } 36 | -------------------------------------------------------------------------------- /src/payroll/hole07/TaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole07; 2 | 3 | public class TaxCalculator { 4 | public long taxFor(final long grossSalary) { 5 | final TaxBand upperTaxBand = new TaxBand(40000, 0.4); 6 | final long upperTaxBracketTax = upperTaxBand.taxInBand(grossSalary); 7 | final long remainingGrossForMiddleAndLowerBrackets = upperTaxBand.grossToTaxInBandsBelowCurrent(grossSalary); 8 | 9 | final TaxBand middleTaxBand = new TaxBand(20000, 0.2); 10 | final long middleTaxBracketTax = middleTaxBand.taxInBand(remainingGrossForMiddleAndLowerBrackets); 11 | final long remainingGrossForLowerBracket = middleTaxBand.grossToTaxInBandsBelowCurrent(remainingGrossForMiddleAndLowerBrackets); 12 | 13 | final TaxBand lowerTaxBand = new TaxBand(5000, 0.1); 14 | final long lowerTaxBracketTax = lowerTaxBand.taxInBand(remainingGrossForLowerBracket); 15 | 16 | return lowerTaxBracketTax + middleTaxBracketTax + upperTaxBracketTax; 17 | } 18 | 19 | private static class TaxBand { 20 | private final long minimumGross; 21 | private final double taxRate; 22 | 23 | private TaxBand(long minimumGross, double taxRate) { 24 | this.minimumGross = minimumGross; 25 | this.taxRate = taxRate; 26 | } 27 | 28 | private long grossToTaxInBand(long grossSalaryExcludingPartAlreadyTaxedAtHigherRate) { 29 | return Math.max(0, grossSalaryExcludingPartAlreadyTaxedAtHigherRate - minimumGross); 30 | } 31 | 32 | private long grossToTaxInBandsBelowCurrent(final long grossSalary) { 33 | return Math.min(grossSalary, minimumGross); 34 | } 35 | 36 | private long taxInBand(final long grossSalaryExcludingPartAlreadyTaxedAtHigherRate) { 37 | return Math.round(grossToTaxInBand(grossSalaryExcludingPartAlreadyTaxedAtHigherRate) * taxRate); 38 | } 39 | } 40 | } 41 | -------------------------------------------------------------------------------- /src/payroll/hole07/notes.md: -------------------------------------------------------------------------------- 1 | This version of `TaxCalculator` is better, but notice that it's still got 2 | repetition in the way the tax bands are used. 3 | Can we make this more regular and simplify the structure? 4 | 5 | -------------------------------------------------------------------------------- /src/payroll/hole08/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole08; 2 | 3 | public class Payslip { 4 | private final long grossSalary; 5 | private final TaxCalculator taxCalculator; 6 | 7 | public Payslip(final long grossSalary, final TaxCalculator taxCalculator) { 8 | this.grossSalary = grossSalary; 9 | this.taxCalculator = taxCalculator; 10 | } 11 | 12 | public long getNet() { 13 | return grossSalary - taxCalculator.taxFor(grossSalary); 14 | } 15 | } 16 | -------------------------------------------------------------------------------- /src/payroll/hole08/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole08; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | assertNetForGross(5000, 5000); 11 | } 12 | 13 | @Test 14 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 15 | assertNetForGross(10000, 9500); 16 | assertNetForGross(20000, 18500); 17 | } 18 | 19 | @Test 20 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 21 | assertNetForGross(25000, 22500); 22 | assertNetForGross(40000, 34500); 23 | } 24 | 25 | @Test 26 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 27 | assertNetForGross(50000, 40500); 28 | assertNetForGross(60000, 46500); 29 | } 30 | 31 | private void assertNetForGross(final int gross, final int expectedNet) { 32 | final Payslip payslip = new Payslip(gross, new TaxCalculator()); 33 | assertEquals(expectedNet, payslip.getNet()); 34 | } 35 | } 36 | -------------------------------------------------------------------------------- /src/payroll/hole08/TaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole08; 2 | 3 | public class TaxCalculator { 4 | public long taxFor(final long grossSalary) { 5 | final TaxBand lowerTaxBand = new TaxBand(5000, 0.1, null); 6 | final TaxBand middleTaxBand = new TaxBand(20000, 0.2, lowerTaxBand); 7 | final TaxBand upperTaxBand = new TaxBand(40000, 0.4, middleTaxBand); 8 | 9 | return upperTaxBand.taxFor(grossSalary); 10 | } 11 | 12 | private static class TaxBand { 13 | private final long minimumGross; 14 | private final double taxRate; 15 | private final TaxBand lowerTaxBand; 16 | 17 | private TaxBand(long minimumGross, double taxRate, TaxBand lowerTaxBand) { 18 | this.minimumGross = minimumGross; 19 | this.taxRate = taxRate; 20 | this.lowerTaxBand = lowerTaxBand; 21 | } 22 | 23 | private long grossInBand(long grossSalary) { 24 | return Math.max(0, grossSalary - minimumGross); 25 | } 26 | 27 | private long grossToTaxAtLowerBand(final long grossSalary) { 28 | return Math.min(grossSalary, minimumGross); 29 | } 30 | 31 | private long taxForBand(final long grossSalary) { 32 | return Math.round(grossInBand(grossSalary) * taxRate); 33 | } 34 | 35 | private long taxForLowerBands(long grossSalary) { 36 | return lowerTaxBand == null ? 0 : lowerTaxBand.taxFor(grossToTaxAtLowerBand(grossSalary)); 37 | } 38 | 39 | private long taxFor(long grossSalary) { 40 | return taxForBand(grossSalary) + taxForLowerBands(grossSalary); 41 | } 42 | } 43 | } 44 | -------------------------------------------------------------------------------- /src/payroll/hole08/notes.md: -------------------------------------------------------------------------------- 1 | The `TaxCalculator` just seems to be a wrapper for the TaxBand. Do we still need it? 2 | -------------------------------------------------------------------------------- /src/payroll/hole09/BandedTaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole09; 2 | 3 | 4 | public class BandedTaxCalculator implements TaxCalculator { 5 | private final long minimumGross; 6 | private final double taxRate; 7 | private final TaxCalculator lowerBandCalculator; 8 | 9 | public BandedTaxCalculator(long minimumGross, double taxRate, TaxCalculator lowerBandCalculator) { 10 | this.minimumGross = minimumGross; 11 | this.taxRate = taxRate; 12 | this.lowerBandCalculator = lowerBandCalculator; 13 | } 14 | 15 | @Override 16 | public long taxFor(long grossSalary) { 17 | return taxForBand(grossSalary) + taxForLowerBands(grossSalary); 18 | } 19 | 20 | private long taxForLowerBands(long grossSalary) { 21 | return lowerBandCalculator == null ? 0 : lowerBandCalculator.taxFor(grossToTaxAtLowerBand(grossSalary)); 22 | } 23 | 24 | private long grossToTaxAtLowerBand(long grossSalary) { 25 | return Math.min(grossSalary, minimumGross); 26 | } 27 | 28 | private long taxForBand(long grossSalary) { 29 | return Math.round(grossInBand(grossSalary) * taxRate); 30 | } 31 | 32 | private long grossInBand(long grossSalary) { 33 | return Math.max(0, grossSalary - minimumGross); 34 | } 35 | } 36 | -------------------------------------------------------------------------------- /src/payroll/hole09/BandedTaxCalculatorTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole09; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class BandedTaxCalculatorTest { 8 | private static final double RATE_FOR_BAND = 0.1; 9 | private static final int MINIMUM_GROSS_FOR_BAND = 1000; 10 | private static final int TAX_FROM_LOWER_BAND = 1; 11 | 12 | private final BandedTaxCalculator calculator = 13 | new BandedTaxCalculator(MINIMUM_GROSS_FOR_BAND, RATE_FOR_BAND, grossSalary -> TAX_FROM_LOWER_BAND); 14 | 15 | @Test 16 | public void lowerBandTaxIsZeroIfLowerBandCalculatorIsNull() { 17 | BandedTaxCalculator calculator = new BandedTaxCalculator(MINIMUM_GROSS_FOR_BAND, RATE_FOR_BAND, null); 18 | assertEquals(RATE_FOR_BAND * (2000 - MINIMUM_GROSS_FOR_BAND), calculator.taxFor(2000), 0); 19 | } 20 | 21 | @Test 22 | public void allTaxIsFromLowerBandsIfGrossSalaryIsLessThanMinimumForBand() { 23 | assertEquals(TAX_FROM_LOWER_BAND, calculator.taxFor(MINIMUM_GROSS_FOR_BAND), 0); 24 | } 25 | 26 | @Test 27 | public void taxIsSumOfTaxFromLowerBandsAndTaxFromThisBand() { 28 | assertEquals(TAX_FROM_LOWER_BAND + RATE_FOR_BAND * (2000 - MINIMUM_GROSS_FOR_BAND), calculator.taxFor(2000), 0); 29 | } 30 | } 31 | -------------------------------------------------------------------------------- /src/payroll/hole09/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole09; 2 | 3 | public class Payslip { 4 | private final long grossSalary; 5 | private final TaxCalculator taxCalculator; 6 | 7 | public Payslip(final long grossSalary, final TaxCalculator taxCalculator) { 8 | this.grossSalary = grossSalary; 9 | this.taxCalculator = taxCalculator; 10 | } 11 | 12 | public long getNet() { 13 | return grossSalary - taxCalculator.taxFor(grossSalary); 14 | } 15 | } 16 | -------------------------------------------------------------------------------- /src/payroll/hole09/PayslipTaxTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole09; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTaxTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | assertNetForGross(5000, 5000); 11 | } 12 | 13 | @Test 14 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 15 | assertNetForGross(10000, 9500); 16 | assertNetForGross(20000, 18500); 17 | } 18 | 19 | @Test 20 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 21 | assertNetForGross(25000, 22500); 22 | assertNetForGross(40000, 34500); 23 | } 24 | 25 | @Test 26 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 27 | assertNetForGross(50000, 40500); 28 | assertNetForGross(60000, 46500); 29 | } 30 | 31 | private void assertNetForGross(final int gross, final int expectedNet) { 32 | final Payslip payslip = new Payslip(gross, 33 | new BandedTaxCalculator(40000, 0.4, 34 | new BandedTaxCalculator(20000, 0.2, 35 | new BandedTaxCalculator(5000, 0.1, null)))); 36 | assertEquals(expectedNet, payslip.getNet()); 37 | } 38 | } 39 | -------------------------------------------------------------------------------- /src/payroll/hole09/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole09; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void netIsGrossMinusTax() { 10 | final Payslip payslip = new Payslip(5000, grossSalary -> 500); 11 | assertEquals(4500, payslip.getNet()); 12 | } 13 | } 14 | -------------------------------------------------------------------------------- /src/payroll/hole09/TaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole09; 2 | 3 | public interface TaxCalculator { 4 | long taxFor(final long grossSalary); 5 | } 6 | -------------------------------------------------------------------------------- /src/payroll/hole09/notes.md: -------------------------------------------------------------------------------- 1 | The check for null in `BandedTaxCalculator` is a bit clumsy. Is there a better way? 2 | 3 | -------------------------------------------------------------------------------- /src/payroll/hole10/BandedTaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole10; 2 | 3 | public class BandedTaxCalculator implements TaxCalculator { 4 | private final long minimumGross; 5 | private final double taxRate; 6 | private final TaxCalculator lowerBandCalculator; 7 | 8 | public BandedTaxCalculator(long minimumGross, double taxRate, TaxCalculator lowerBandCalculator) { 9 | this.minimumGross = minimumGross; 10 | this.taxRate = taxRate; 11 | this.lowerBandCalculator = lowerBandCalculator; 12 | } 13 | 14 | @Override 15 | public long taxFor(long grossSalary) { 16 | return taxForBand(grossSalary) + getTaxForLowerBands(grossSalary); 17 | } 18 | 19 | private long getTaxForLowerBands(long grossSalary) { 20 | return lowerBandCalculator.taxFor(grossToTaxAtLowerBand(grossSalary)); 21 | } 22 | 23 | private long grossToTaxAtLowerBand(long grossSalary) { 24 | return Math.min(grossSalary, minimumGross); 25 | } 26 | 27 | private long taxForBand(long grossSalary) { 28 | return Math.round(grossInBand(grossSalary) * taxRate); 29 | } 30 | 31 | private long grossInBand(long grossSalary) { 32 | return Math.max(0, grossSalary - minimumGross); 33 | } 34 | } 35 | -------------------------------------------------------------------------------- /src/payroll/hole10/NullTaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole10; 2 | 3 | public class NullTaxCalculator implements TaxCalculator { 4 | @Override 5 | public long taxFor(long grossSalary) { 6 | return 0; 7 | } 8 | } 9 | -------------------------------------------------------------------------------- /src/payroll/hole10/Payslip.java: -------------------------------------------------------------------------------- 1 | package payroll.hole10; 2 | 3 | public class Payslip { 4 | private final long grossSalary; 5 | private final TaxCalculator taxCalculator; 6 | 7 | public Payslip(final long grossSalary, final TaxCalculator taxCalculator) { 8 | this.grossSalary = grossSalary; 9 | this.taxCalculator = taxCalculator; 10 | } 11 | 12 | public long getNet() { 13 | return grossSalary - taxCalculator.taxFor(grossSalary); 14 | } 15 | } 16 | -------------------------------------------------------------------------------- /src/payroll/hole10/PayslipTaxTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole10; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTaxTest { 8 | @Test 9 | public void taxIsZeroIfGrossIsBelowTaxFreeLimit() { 10 | assertNetForGross(5000, 5000); 11 | } 12 | 13 | @Test 14 | public void taxOnAmountInLowerTaxBracketExcludesTaxFreeLimit() { 15 | assertNetForGross(10000, 9500); 16 | assertNetForGross(20000, 18500); 17 | } 18 | 19 | @Test 20 | public void taxOnAmountInMiddleTaxBracketIsSumOfLowerTaxBracketAmountAndAdditionalMiddleTaxBracketAmount() { 21 | assertNetForGross(25000, 22500); 22 | assertNetForGross(40000, 34500); 23 | } 24 | 25 | @Test 26 | public void taxOnAmountInUpperTaxBracketIsSumOfLowerTaxBracketAmountAndMiddleTaxBracketAmountAndAdditionalUpperTaxBracketAmount() { 27 | assertNetForGross(50000, 40500); 28 | assertNetForGross(60000, 46500); 29 | } 30 | 31 | private void assertNetForGross(final int gross, final int expectedNet) { 32 | final Payslip payslip = new Payslip(gross, 33 | new BandedTaxCalculator(40000, 0.4, 34 | new BandedTaxCalculator(20000, 0.2, 35 | new BandedTaxCalculator(5000, 0.1, 36 | new NullTaxCalculator())))); 37 | assertEquals(expectedNet, payslip.getNet(), 1e-6); 38 | } 39 | } 40 | -------------------------------------------------------------------------------- /src/payroll/hole10/PayslipTest.java: -------------------------------------------------------------------------------- 1 | package payroll.hole10; 2 | 3 | import org.junit.Test; 4 | 5 | import static org.junit.Assert.assertEquals; 6 | 7 | public class PayslipTest { 8 | @Test 9 | public void netIsGrossMinusTax() { 10 | final Payslip payslip = new Payslip(5000, grossSalary -> 500); 11 | assertEquals(4500, payslip.getNet()); 12 | } 13 | } 14 | -------------------------------------------------------------------------------- /src/payroll/hole10/TaxCalculator.java: -------------------------------------------------------------------------------- 1 | package payroll.hole10; 2 | 3 | public interface TaxCalculator { 4 | long taxFor(final long grossSalary); 5 | } 6 | --------------------------------------------------------------------------------