Logging while Testing

Sometimes we need to write logging statements to give a little more context when things go wrong. In Kotest we provide the standard logging functions in the scope of each test that one would expect: error, warn, info, debug, and trace. Each function accepts an expression that is only executed when the configured logging level or greater is set by config, e.g.: warn { "foo" } would be executed if kotest.framework.loglevel=info.

Setup

In order to get logging working you'll need two things:

1. at least one implementation of LogExtension added to extensions in your AbstractProjectConfig
2. a configured value for logLevel added to your AbstractProjectConfig, or set using the sysprop or environment variable kotest.framework.loglevel

Note: the sysprop and environment variable will override the setting in your AbstractProjectConfig

object ProjectConfig : AbstractProjectConfig() {
    override val logLevel = LogLevel.Error
    override fun extensions() = listOf(
        object : LogExtension {
            override suspend fun handleLogs(testCase: TestCase, logs: List<LogEntry>) {
                logs.forEach { println(it.level.name + " - " + it.message) }
            }
        }
    )
}

Usage

Now you can just log using the aforementioned extension methods on the Kotest TestScope

test("test something") {
  warn { "something weird happened" }
}

Additionally, we provide a logger object to pass around your tests, in the case that you write a test function

test("test something else") {
  logger.assertSomething("something else")
}

fun TestLogger.assertSomething(actual: String) {
   info { "asserting something about $actual" }
}