Testing

Kermit includes a test dependency, intended for use when testing application code that interacts with Kermit APIs but doesn't want to write to actual logs. This includes a TestLogWriter which holds the string outputs of log statements, and has APIs for asserting on what logs are present.

note

The test APIs are not yet stable, and require opting into the @ExperimentalKermitApi annotation. The current API is based on what we use to test Kermit internally. It may change dramatically before we stabilize it as we consider more real-world use-cases.

Add to your dependencies

Typically you would depend on this from your test sources.

sourceSets {
    commonTest {
        dependencies {
            implementation("co.touchlab:kermit-test:2.0.3") //Add latest version
        }
    }
}

Use in your tests

info

We strongly recommend you inject logger instances into your classes rather than simply calling the (global) static Logger as it will make testing easier.

Suppose you have a test

@OptIn(ExperimentalKermitApi::class)
class MyExampleTest {
    private val testLogWriter = TestLogWriter(
        loggable = Severity.Verbose // accept everything
    )
    private val kermit = Logger(
        TestConfig(
            minSeverity = Severity.Debug,
            logWriterList = listOf(testLogWriter)
        )
    )
    
    // ...
}

You can either interact with the latest log entry that was produced -

@Test
fun somethingInterestingHappened() {
    // ...

    testLogWriter.assertCount(1)

    // calls assertTrue() on the result of the lambda
    testLogWriter.assertLast {
        message == "the message" && severity == Severity.Info && tag == "my-tag" && throwable == null
    }
}

or you can interact with the list of log entries directly

@Test
fun somethingElseInterestingHappened() {
    // ...

    testLogWriter.assertCount(10)

    with(testLogWriter.logs[3]) {
        assertEquals("the message", message)
        assertEquals(Severity.Info, severity)
        assertEquals("my-tag", tag)
        assertNull(throwable)
    }
}

Logging on Android

The default setup of Kermit aims to make production logging as simple as possible. This means that the platform logger for Android defaults to passing the log through to Android's logcat Log() method. Be sure to configure your tests accordingly, as this wont function when running unit tests on your local machine!