Junit - how to get test result as string? - kotlin

Question

I am trying to test the code and get a result as String to send it to API later.
class FirstClass{
fun main(){
print("Hello world!")
}
}
Test:
ort org.junit.jupiter.api.AfterEach
import org.junit.jupiter.api.BeforeEach
import org.junit.jupiter.api.Test
import java.io.ByteArrayOutputStream
import java.io.PrintStream
import kotlin.test.assertEquals
internal class FirstClassTest {
private val outContent = ByteArrayOutputStream()
private val errContent = ByteArrayOutputStream()
private val originalOut = System.out
private val originalErr = System.err
#BeforeEach
fun setUp() {
System.setOut(PrintStream(outContent))
System.setErr(PrintStream(errContent))
}
#AfterEach
fun tearDown() {
System.setOut(originalOut)
System.setErr(originalErr)
}
#Test
fun main() {
val SUT = FirstClass()
SUT.main()
val testResult = assertEquals("Hello world!", outContent.toString())
print("Test result: $testResult")
val api = Api()
val apiResult = api.sendResult(testResult.toString())
print("Api result: $apiResult")
}
}
The test is passing, however, I do not see printed messages. How to get a test result as String?

Answer 1

There are several issues here.  The main one is:
The redirection affects your test method too.
Because you've redirected System.out, the print() in your test method goes to outContent, along with the output from FirstClass.main() that you want to test, instead of to the screen or wherever you want it.
I can see two fixes for this.
The quick one is for your test method to output to originalOut:
originalOut.print("Test result: $testResult")
Your test method is in the class which does the redirection, so there's no problem with it knowing about the redirection, and it already has access to originalOut.
However, if you can, I think a better solution is to refactor FirstClass so that it doesn't hard-code the stream it writes to.  For example, the stream could be passed as a parameter; or it could return the string directly (and the caller, in a thin non-tested wrapper, could write it to System.out).
That would be more work, but would make your code more flexible as well as easier to test.
Other issues include:
You're using print() instead of println().
Many streams are line-buffered, writing their output only after a newline, and so you might not see any results if there isn't one.  (And even if you do, all the results would be jammed on a single line!)
You assign the result of assertEquals().
assertEquals() doesn't have a useful return value.  (It return Unit.)  So your code will simply show:
Test result: kotlin.Unit
Instead, like all the assert functions, it throws an exception if the assertion fails.  So there's no point in storing or processing the return value; simply calling the assertion is enough.
— This means that there's usually no need to call print()/println() from your test method anyway!  If there's a failure, it'll be obvious: running from the command line will stop with an exception message and stack trace; IntelliJ shows a big red mark next to that test; Maven and Gradle will stop the build (after all tests have run), showing the number of failures.  So if everything continues smoothly, you know the tests have passed.
Api is not defined.
The code you posted above won't compile, because it doesn't include a definition or import for Api.  (Those last lines can be removed, though, without affecting the question.)
main() is a confusing name for a test.
The unit testing framework will find and run all test methods annotated with #Test.  A test class will often contain many different test methods, and it's usual to name them after the aspect they're testing.  (That makes any failures clearer.)  Calling it main() not only fails to describe what's being tested, but also suggests that the method will be run from outside the testing framework, which would probably not behave properly.