ExpenseReport
The ExpenseReport legacy code refactoring kata in various languages.
This is an example of a piece of legacy code with lots of code smells.
The goal is to support the following new feature as best as you can:
- Add Lunch with an expense limit of 2000.
Process
- ๐ Read the code to understand what it does and how it works.
- ๐ฆจ Read the code and check for design and code smells. Make a list of all code and design smells that you find.
- ๐งโ๐ฌ Analyze what you would have to change to implement the new requirement without refactoring the code.
- ๐งช Write a characterization test. Expand your list of code and design smells. Add those smells that you missed earlier and discovered now because they made your life writing a test miserable.
- ๐ง Refactor the code.
- ๐ง Refactor the test.
- ๐ผ Test-drive the new feature.
Supported Languages
The ExpenseReport example currently exists in the following languages:
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Ada
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Assembler (Motorola 68020, Amiga OS, MaxonASM)
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Assembler (AArch64, Linux, GNU Assembler)
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Assembler (AMD64/Intel x86-64, Linux, GNU Assembler)
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bash
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BASIC (Amiga BASIC, Commodore Amiga) โ Quite amazing! First BASIC without line numbers!
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BASIC (Bywater BASIC, Linux) (very similar to Commodore BASIC)
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BASIC (Commodore BASIC, Commodore 64)
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BASIC (Locomotive BASIC, Amstrad CPC)
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BASIC (Yabasic)
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C
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C#
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C++
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Clojure โ This one was particularly painful to intentionally write poorly, I almost cried.
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COBOL
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D
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Dart
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Elixir
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F#
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Fortran
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Go
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Groovy
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Haskell
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Java
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JavaScript
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Julia
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Kotlin
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Lisp (Common Lisp)
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Lua
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Nim
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Objective-C
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Pascal
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Perl
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PHP
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PostScript
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Prolog
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Python
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Raku (Perl6)
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Rexx (tested with Regina Rexx and ARexx)
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Ruby
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Rust
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Scala
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Scheme
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Smalltalk
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SQL (Using SQLite3)
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Swift
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TcL
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TypeScript
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Visual BASIC
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XML/XSLT
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Zig
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zsh
Planned languages
(in no particular order and with no guarantee)
- ABAP
- Amiga E
- AMOS BASIC
- APL
- More Assembler implementations (arm, aarch64, i686, powerpc, powerpc64, mpis, mips64, sparc, sparc64, risc-v, etc, usually on Linux)
- Carbon
- CLIPS
- Cluster
- Concurnas
- Curry
- Dark
- Eiffel
- Elm
- Erlang
- Flix
- Forth
- Gleam
- Gosu
- Hack
- Hare
- Java Byte Code / JVM Assembler
- Lobster
- Logo
- Mercury
- Modula-2 (once the linker starts working again)
- Mojo
- Oberon
- OCaml
- Pony
- PureScript
- R
- Reason
- REBOL
- Scratch
- SNOBOL
- Solidity (maybe)
- Strongtalk
- TeX
- Unison
- WebAssembly
Languages explicitly not planned
- Brainfuck
- False
- Malbolge
- Whitespace
Undecided Languages
There are many more programming languages than in the list above.
Find a more complete list on Wikipedia.
Other plans
- Make sure that all languages are providing the identical challenge.
To be practical, this will require the removal of the timestamp side-effect.
- Provide the time-stamp side-effect on a separate branch.
- Provide a test setup (without test) on a separate branch so that folks can choose whether they want to include the setup work in the kata or not.
- Provide a level 2 challenge for creating an HTML report besides the Plain Text report.
Solutions
To see solutions, switch to the solutions branch.
Warning The solutions branch will be rebased!
Credits and License
I first encountered the ExpenseReport example during a bootcamp at Equal Experts.
I also have seen the ExpenseReport example being used by Robert "Uncle Bob" C. Martin.
However, he seems to not be the original author (https://twitter.com/unclebobmartin/status/1537063143326855176?s=20&t=lh_vVb9jUQmY6PYG50974w)
I have tried to research its origins but so far I have failed.
If you know who has first come up with this example, please get in touch with me.
As I was asked for the license conditions, I have decided to put this under CC-BY-SA, with the following considerations:
- Please credit me, last but not least to retain the opportunity for people to experience this exercise in as many programming languages as they are interested in.
- Share it under the same license.
- Using this as training material should be allowed, even if the trainer is charging money for their time.
Disclaimer: As stated above, I did not come up with the original version.
The original author is unknown to me.
The CC-BY-SA license thus can only cover my contribution: Recreating the Java version from memory, creating the versions in other programming languages than Java, and keeping them consistent.