How redirect Timber logs to Junit logcat

Question

I'm using Timber with a DebugTree and a ProductionTree. All is fine and perfect in the running app. I also succeed to use Timber in my JUnit test implementation, and that's fine (no real benefit, but it does work).

However, I would like to get the logs on the code under test to be displayed in the JUnit log.

I tried to build a JUnitTree and redirect timber logs to println(…), and setup the Timber JUnitTree in @Before function, but nothing worked. Any solution from the community?

Does my request make no sens, I didn't find anything about this need in the web (maybe I used wrong keywords).

Answer 1

The following ConsoleTree class can be used to forward Timber logs to standard output:

class ConsoleTree : Timber.DebugTree() {

    @Language("RegExp")
    private val anonymousClassPattern = Pattern.compile("""(\$\d+)+$""")

    private val dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS")

    override fun log(priority: Int, tag: String?, message: String, throwable: Throwable?) {
        val dateTime = LocalDateTime.now().formatWith(dateTimeFormatter)
        val priorityChar = when (priority) {
            Log.VERBOSE -> 'V'
            Log.DEBUG -> 'D'
            Log.INFO -> 'I'
            Log.WARN -> 'W'
            Log.ERROR -> 'E'
            Log.ASSERT -> 'A'
            else -> '?'
        }

        println("$dateTime $priorityChar/$tag: $message")
    }

    override fun createStackElementTag(element: StackTraceElement): String? {
        val matcher = anonymousClassPattern.matcher(element.className)
        val tag = when {
            matcher.find() -> matcher.replaceAll("")
            else -> element.className
        }
        return tag.substringAfterLast('.')
    }
}

For JUnit 4 a rule can be used to plant and uproot ConsoleTree automatically for each test:

class TimberConsoleRule : TestRule {
    override fun apply(base: Statement, description: Description) =
        TimberConsoleStatement(base)
}

class TimberConsoleStatement constructor(private val baseStatement: Statement) : Statement() {

    private val consoleTree = ConsoleTree()

    override fun evaluate() {
        Timber.plant(consoleTree)
        try {
            baseStatement.evaluate()
        } finally {
            Timber.uproot(consoleTree)
        }
    }
}

For JUnit 5 you can simply annotate JUnit test with the following @TimberConsoleLog annotation:

@ExtendWith(TimberConsoleExtension::class)
@Retention(RUNTIME)
annotation class TimberConsoleLog

class TimberConsoleExtension : BeforeAllCallback, AfterAllCallback {

    private val consoleTree = ConsoleTree()

    override fun beforeAll(context: ExtensionContext) =
        Timber.plant(consoleTree)

    override fun afterAll(context: ExtensionContext) = 
        Timber.uproot(consoleTree)
}