Grails spock Testing with File class - unit-testing

Question

I have a method that create a file based in a content copied from an another file.
Like below
private cloneBaseFile(fileName, ddi, ddd){
def config = grailsApplication.config.kicksim.fileConstants
String baseFileContents = new File(config.baseFile).getText('UTF-8')
def help = handleString("${ddd}.${ddi}")
baseFileContents = baseFileContents.replaceAll("DDDDDI", help);
def f1= new File(fileName)
f1 << baseFileContents
return fileName
}
I'd like to know how to unit test it.

Answer 1

I think you should look to separate out the responsibilities of this method (c.f. Single Responsibility Principle). If you haven't got a copy of Robert Martin's book called Clean Code then I'd highly recommend it: his code is a work of art and taught me a lot.
cloneBaseFile() is actually doing many things: it's opening a file, getting the contents of the file, doing something (I don't know what) in handleString(), replacing the contents of the file with a modified version of its contents and then finally saving the file.
How about (as a starter for 10):
private cloneBaseFile(fileName, ddi, ddd){
def config = grailsApplication.config.kicksim.fileConstants
String baseFileContents = getFileContents(config.baseFile)
baseFileContents = handleFileContents(baseFileContents)
return createNewFileWithContents(fileName, baseFileContents)
}
String getFileContents(String fileName) {
String contents = new File(fileName).getText('UTF-8')
return contents
}
String handleFileContents(String oldContents) {
def help = handleString("${ddd}.${ddi}")
return oldContents.replaceAll("DDDDDI", help);
}
String createNewFileWithContents(String newFileName, String newContents) {
def f1= new File(newFileName)
f1 << newContents
return newFileName
}
Now you have multiple small methods, each of which can be tested far more easily. You'll also want to test the handleString() method.