Proposed Solution Day 22.

Author: yanncourtel

README.md

@@ -93,6 +93,7 @@ A solution proposal will be published here every day during the `Advent Of Craft
 - [Day 19: Loosing up dead weight.](solution/day19/docs/step-by-step.md)
 - [Day 20: No more exceptions in our domain.](solution/day20/docs/step-by-step.md)
 - [Day 21: Refactor the tests and production code to Output-Based tests.](solution/day21/docs/step-by-step.md)
+- [Day 22: Design a diamond program using T.D.D and Property-Based Testing.](solution/day22/docs/step-by-step.md)
 
 ## Contributors
 

solution/day22/.tcr/config.yml

@@ -0,0 +1,9 @@
+config:
+  git:
+    auto-push: false
+    polling-period: 2s
+  mob-timer:
+    duration: 5m0s
+  tcr:
+    language: java
+    toolchain: maven

solution/day22/.tcr/language/java.yml

@@ -0,0 +1,9 @@
+toolchains:
+  default: maven
+  compatible-with: [ maven ]
+source-files:
+  directories: [ src/main ]
+  patterns: [ '(?i)^.*\.java$' ]
+test-files:
+  directories: [ src/test ]
+  patterns: [ '(?i)^.*\.java$' ]

solution/day22/.tcr/toolchain/maven.yml

@@ -0,0 +1,11 @@
+build:
+  - os: [ darwin, linux, windows ]
+    arch: [ "386", amd64, arm64 ]
+    command: mvn
+    arguments: [ test-compile ]
+test:
+  - os: [ darwin, linux, windows ]
+    arch: [ "386", amd64, arm64 ]
+    command: mvn
+    arguments: [ test ]
+test-result-dir: target/surefire-reports

solution/day22/docs/challenge-done.md

@@ -0,0 +1,120 @@
+## Day 22: Design a diamond program using T.D.D and Property-Based Testing.
+
+We think about a possible contract for our class:
+- It may contain a `print` method taking the `endCharacter` as parameter
+  - It could look like `Character` -> `Option<String>`
+  - We could use an `Option` because there are some cases that are not supported (ex: '^', '1', ...)
+
+Let's design and implement it starting from less to more complex properties.
+
+### None for invalid characters
+
+```text
+for all (invalidEndCharacter)
+such that print(invalidEndCharacter) fail
+```
+
+🔴 We start by creating this first property
+
+- We can generate production code from the `property`
+- We work on how to generate `invalidEndCharacters`
+- We check the generation of random characters
+  - Here is an example of values
+
+🟢 We make it pass by `hardcoding` the result
+
+🔵 We clean a little bit the test
+
+### Horizontally symmetric
+
+```text
+for all (validEndCharacter)
+such that diamond(validEndCharacter) == reverse(diamond(validEndCharacter))
+```
+
+🔴 We add a first version of the property
+
+🟢 We make it pass by `hardcoding` the return value
+
+🔵 We extract the guard and use ternary operator
+
+### Is a square  (height = width)
+
+```text
+for all (validEndCharacter)
+such that diamond(validEndCharacter) is a square
+```
+
+The result `String` should a square meaning that each line contains the same number of characters than the number of lines.
+
+🔴 Let's identify if it is a square
+
+🟢 We can make it pass by simply returning 'A'
+
+🔵 We have plenty of duplication in our tests
+
+### Contain 2 identical letters per line
+
+```text
+for all (validEndCharacter)
+such that each line in diamond(validEndCharacter) contains 2 identical letters except first and last 
+```
+
+😬 It is already green...
+
+It is maybe a signal that we need to iterate on the implementation
+
+- We design from the implementation
+
+🔴 Our properties are now failing, we can triangulate the algorithm
+
+- We experiment and learn from the properties
+- We fix the property `be_horizontally_symmetric` by iterating on the code
+- We fix `contains_2_letters_per_line` by fixing the `toLine` method
+- We fix the property `be_a_square` by fixing the `generateEmptyCharacters`
+
+🟢 All our properties are green again 🤩
+
+🔵 Let's refactor our `Diamond` to extract some method and give business names
+
+### Lines have a decreasing number of left spaces
+
+```text
+for all (validEndCharacter)
+such that Lines have a decreasing number of left white spaces until end character 
+```
+
+🟢 Not that easy to create...
+
+🔵 We refactor the test to make it more clear what we do in it
+
+### Lines have a decreasing number of right spaces
+
+🟢 As you may expect the property is green
+
+🔵 We can remove duplications in the test
+
+- We create a new `method` to centralize this logic
+
+> All our properties are green 🤩. Are we confident enough?
+
+### Add an `Approval` test
+
+To increase our confidence we secure our implementation with a `Unit Test`.
+We choose to use an `Approval` one.
+
+🔴 It fails because we need to approve the result
+
+🟢 It seems pretty good
+
+We approve the file, and we're done, for now 😉.
+
+Our `Diamond` is complete!
+
+>**Tip of the day: Property based testing with TDD can help you design a more robust implementation.**
+
+### Share your experience
+
+How does your code look like?
+
+Please let everyone know in the discord.