[gradle-testkit-truth] More useful error messages

[BraisGabin]

I'm adding gradle-testkit-truth to my project and it works fine when the tests passes but when the things go wrong the message is not that useful.

With this code assertThat(buildResult).task(":lightsaberChecka").failed() I get this message error:

value of                : buildResult.task(:lightsaberChecka)
expected to have a value: FAILED
but was                 : null
buildResult was         : org.gradle.testkit.runner.internal.FeatureCheckBuildResult@3670f00

org.gradle.testkit.runner.internal.FeatureCheckBuildResult@3670f00 gives no information about what's going on.

I would print the output as the "actual" value to provide this information.

Also task(":lightsaberChecka") provides a Subject of a null instance that is not that useful. I think that something like this would improve the error message:

https://github.com/SchwarzIT/dagger-lightsaber/blob/98686ec190168c7f14fed377651c4024af8b9788/gradle-plugin/src/functionalTest/kotlin/schwarz/it/lightsaber/gradle/truth/BuildResultSubject.kt#L17-L23

With this I get error messages like this:

value of:
    buildResult.getTasks()
expected to contain:
    :lightsaberChecka
but was:
    [:compileJava, :processResources, :classes, :compileTestJava, :lightsaberCheck]
buildResult was:
    > Task :compileJava
    > Task :processResources NO-SOURCE
    > Task :classes
    > Task :compileTestJava NO-SOURCE
...

As you can see I have something similar implemented already but I like the idea of having a truth library for this so I can contribute to this library if you think that things like this are valuable.

[autonomousapps]

Thanks for the issue. If you want to contribute these improvements, I would definitely appreciate it! <3