Put exercise generation under test (#426)

* Put exercise generation under test

This change alters `ExercismGenerator` just enough to allow side effect free
tests. Having the class under test enables future refactoring. Three dependencies
made this class difficult to test:
- `PipeableOSProcess` executed commands outside of the Pharo VM
- `ExTonelWriter` wrote files to the OS filesystem
- `ExercismExercise` would access a variable number of exercises depending on how many were implemented

To get this class under test the above dependencies have been placed in lazy
assigned instance variables. This allows tests to assign mocks to the generator
instance.

There are two mock OS processes, one that always succeeds, and one that always fails.
Neither executes any function outside the VM.

A  `ExTonelWriter` writes exercises to an in memory file system that lasts only
for the test.

A mock exercism exercise class returns only a single exercise. This speeds up the
test and makes it more consistent as it won't change when more exercises are implemented.

## Test Issues with Line Endings

When run in CI (Ubuntu 16.04) one of the tests failed, but the same test passed on my personal computer (MacOS).

I suspect that even though the tests use an in memory file system, OS specific line-feed and carriage-return
characters will be used. This causes enough of a difference between the expected result and the actual
result that the outcome will be a failed test. Each test that works with an in memory file system will normalize the
line endings of the expected result and the actual result to the same character. This should eliminate this kind of
environment specific failure in tests.

The test design closely follows that of `TonelWriterTest` which also uses an in memory file system.

dev/src/ExercismDev/ExercismGenerator.class.st

@@ -1,17 +1,50 @@
 "
-I am responsible for generating kebab-cased Exercism edirectories, each containing a seperate exercise for users.
+# ExercismGenerator
 
-We have to do it this way as Exercism conventions differ from Tonel, and so we need to output them to a seperate directory suitable for  the Exercism command line tool.
+I am responsible for generating kebab-cased Exercism V2 directories, each containing a seperate exercise for users.
+
+Exercism requires plain text files that can be served to the website as exercises and then downloaded for a student 
+to work on. We have to do it this way as Exercism conventions differ from Tonel, and so we need to output them to a 
+seperate directory suitable for the Exercism command line tool.
+
+## Collaborators
+
+I need two other key objects to do my job: an `ExTonelWriter` and a `PipeableOSProcess`. `ExTonelWriter` does the
+actual job of writing Tonel format files to disk. `PipeableOSProcess` is needed to make a external command line
+call to the configlet tool.
+
+To grab the exercises that need to be written I use `ExercismExercise`.
+
+## Usage
 
 When you have created a new exercise(s) that you are happy with, you need to run a generation.
 
-You can either click on the #generate example method and be prompted for a file location or evaluate the following  (where the path is one that points to where you have checked out the entire pharo project using either the command line or a git tool):
+You can either run the `ExercismGenerator class>>#generate` method and be prompted for a file location or evaluate 
+the following (where the path is one that points to where you have checked out the entire pharo project using either 
+the command line or a git tool):
 
+```
 ExercismGenerator generateTo: (FileLocator home / 'Dev/Exercism/pharo-git') pathString
+```
+
+## Instance Variables
+
+- exercismExercise: A class handle for easily getting all the implemented exercises. Defaults to `ExercismExercise`.
+- exTonelWriter: `ExTonelWriter`; Responsible for writing objects as Tonel format source text files to the give file path.
+- osProcess: A class handle of an operating system process, for sending external commands.
+
+## Class Variables
+
+- DefaultPath: The default file path that Tonel files will be written to.
 "
 Class {
 	#name : #ExercismGenerator,
 	#superclass : #Object,
+	#instVars : [
+		'exTonelWriter',
+		'osProcess',
+		'exercismExercise'
+	],
 	#classVars : [
 		'DefaultPath'
 	],
@@ -55,6 +88,58 @@ ExercismGenerator >> createTagSnapshotFor: packageOrTag [
 					[ :mc | mc className isNil or: [ mc actualClass category endsWith: packageOrTag name ] ])
 ]
 
+{ #category : #accessing }
+ExercismGenerator >> exTonelWriter [
+
+	^ exTonelWriter 
+		ifNotNil: [ exTonelWriter  ] 
+		ifNil: [ 
+			exTonelWriter := ExTonelWriter.
+			exTonelWriter  
+			 ] 
+]
+
+{ #category : #accessing }
+ExercismGenerator >> exTonelWriter: anExTonelWriter [ 
+
+	exTonelWriter := anExTonelWriter
+]
+
+{ #category : #accessing }
+ExercismGenerator >> exercismExercise [
+
+	^ exercismExercise 
+		ifNotNil: [ exercismExercise ] 
+		ifNil: [ 
+			exercismExercise := ExercismExercise.
+			ExercismExercise  
+			]
+]
+
+{ #category : #accessing }
+ExercismGenerator >> exercismExercise: anExerciseClass [
+
+	exercismExercise := anExerciseClass 
+]
+
+{ #category : #generation }
+ExercismGenerator >> generate [
+	| cmd result basePathReference |
+
+	self exercismExercise allExercises select: [:ex | ex isActive ] thenDo: [:ex |
+			self generateSourceFilesFor: ex exercisePackage to: self class defaultPath ].
+
+	basePathReference := self class defaultPath parent.
+	ExercismConfigGenerator generateTo: basePathReference.
+
+	cmd := 'configlet generate ', (basePathReference pathString surroundedBySingleQuotes).		
+	result := self osProcess waitForCommand: cmd.
+
+	result succeeded
+		ifFalse: [ 
+			self error: 'failure running "configlet generate" - ' , result outputAndError printString ]
+]
+
 { #category : #helper }
 ExercismGenerator >> generateCustomDataFor: anExercismExercise to: destinationDirectory [
 	"Generate markdown hints, that exercism configlet will pickup for readme.md files
@@ -114,8 +199,8 @@ ExercismGenerator >> generateSourceFilesFor: packageOrTag to: filePathString [
 	
 	exerciseDirectoryRef ensureCreateDirectory.
 	exerciseDirectoryRef deleteAll.
-	
-	(ExTonelWriter on: exampleDirectoryRef)
+
+	self exTonelWriter
 		sourceDirectory: (solutionDirectoryRef relativeTo: exampleDirectoryRef) pathString;
 		writeSnapshot: (self createTagSnapshotFor: packageOrTag).
 
@@ -154,3 +239,20 @@ ExercismGenerator >> generateTo: filePathReference [
 		ifFalse: [ 
 			self error: 'failure running "configlet generate" - ' , result outputAndError printString ]
 ]
+
+{ #category : #accessing }
+ExercismGenerator >> osProcess [
+
+	^ osProcess 
+		ifNotNil: [ osProcess ] 
+		ifNil: [ 
+			osProcess := PipeableOSProcess.
+			osProcess  
+			 ] 
+]
+
+{ #category : #accessing }
+ExercismGenerator >> osProcess: anOsProcess [ 
+
+	osProcess := anOsProcess
+]