Has anyone ever tested a stream and `.doOnError *{...

# android

[lawlorslaw]

Has anyone ever tested a stream and .doOnError *{}* doesn't get triggered in a Unit Test. I'm using the Mono from the projectreactor project. It basically functions like a reactive stream. What am i missing?

[lawlorslaw]

I just asked ChatGPT and found out it was because i need to use StepVerifier and now I get into the doOnError{} block. The longer explanation is below :

To test for exceptions in a Mono from Reactor Core, you can use the StepVerifier class to verify the behavior of the Mono. Here’s an example of how you can test for exceptions:

import org.junit.jupiter.api.Test
import reactor.core.publisher.Mono
import reactor.test.StepVerifier

class MonoExceptionTest {

    @Test
    fun testMonoException() {
        val mono: Mono<String> = Mono.error(RuntimeException("Test exception"))

        StepVerifier.create(mono)
            .expectError(RuntimeException::class.java)
            .verify()
    }
}

In this example, the Mono.error method is used to create a Mono that emits an exception when subscribed to. The StepVerifier is then used to verify the behavior of the Mono. The expectError method is called to specify that an error is expected to be emitted by the Mono, and the expected exception type (RuntimeException in this case) is provided as a parameter.
Finally, the verify method is called to start the verification process. If the Mono emits the expected error, the test will pass; otherwise, it will fail.
You can customize the expected exception type by changing the parameter of the expectError method to the specific exception class you want to test.
Note that using verify() will wait for the Mono to complete or emit an error. If you want to assert more details about the exception, you can chain additional methods like assertErrorMessage or assertErrorMatches after the expectError method to further refine your assertions.