How to unit test a method returning Uni/Multi of Smallrye mutiny reactive library?

Question

I am using Smallrye Mutiniy reactive library in my Quarks application as it is supported natively in Quarks applications.

I'am trying to write unit tests for a service class. I am not sure how to write unit tests for a method that returns Uni/Multi.

A method returning Uni<String>

public Uni<String> hello(final String name) {
    final String message = "Hello " + name;
    return Uni.createFrom().item(message);
}

Unit implemented for the above method

@Test
void testHello() {
    final Uni<String> casePass = hello("Ram");
    // assertion passes and all good with this.
    casePass.subscribe().with(message -> Assertions.assertEquals("Hello Ram", message));
    
    final Uni<String> caseFail = hello("Ravan");
    //  It is expected to fail the assertion, and it does. But the test is not failing, instead aseertion fail message simply logged to the console.
    caseFail.subscribe().with(message -> Assertions.assertEquals("Hello Sita", message));
}

Console logs

[-- Mutiny had to drop the following exception --]
Exception received by: io.smallrye.mutiny.helpers.UniCallbackSubscriber.onItem(UniCallbackSubscriber.java:71)
org.opentest4j.AssertionFailedError: expected: <Hello Sita> but was: <Hello Ram>
    at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:55)
    at org.junit.jupiter.api.AssertionUtils.failNotEqual(AssertionUtils.java:62)
    at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:182)
    at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
    at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1124)
...

Answer 1

I would really recommend using the way of testing from SmallRey.

https://smallrye.io/smallrye-mutiny/1.7.0/guides/testing/

You still can get the object out of the multi/uni use invoke, for example.

 public static Uni<String> hello(final String name) {
    final String message = "Hello " + name;
    return Uni.createFrom().item(message);
}

@Test
public void testUnit() {
    UniAssertSubscriber<String> tester = hello("someone")
            .invoke( i -> Assertions.assertEquals("Hello someone", i))
            .invoke(i -> Assertions.assertNotNull(i))
            .subscribe().withSubscriber(UniAssertSubscriber.create());
    tester.assertCompleted();
}

@Test
public void secondUnit() {
    UniAssertSubscriber<String> tester = hello("none")
            .invoke( i -> Assertions.assertEquals("Hello someone", i))
            .invoke(i -> Assertions.assertNotNull(i))
            .subscribe().withSubscriber(UniAssertSubscriber.create());
    tester.assertCompleted();
}

I hope you can use it like that