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)
...

@Ladicek answer is right, But my requirement wasn't that simple. I posted a simple analogous example of the issue facing, a method returning Uni. To get the real object out of Uni and perform complex assertions on composing instances. this is what I had to call uniOfAcomplexObject.subscribe().assertCompleted().withSubscriber(UniAssertSubscriber.create()).getItem() I get the real instance wrapped in Uni/Multi, then I can perform the assertions as I do with normal objects. — Player_Neo, Jul 11 '21 at 14:01

score 6 · Answer 1 · edited Sep 18 '22 at 03:34

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

score 4 · Accepted Answer · answered Jul 14 '21 at 06:53

There are several approaches. You can use the utility methods provided in smallrye.io/smallrye-mutiny/guides/testing. However, if, according to your comment, you need more, I would recommend the following approach:

final Uni<Greeting> casePass = hello("Ram");
Greeting g = casePAss.await().atMost(Duration.ofSeconds(5)); // To be sure we don't stay tucked
// Assertions come here

So basically, you block until the item is sent. Avoid await().indefinitely() because it may block your test if the Uni never send an item. Not that await()... throws an exception if the Uni sends a failure.

This is throwning an error, as it is blocking the event loop thread — Marian Klühspies, Feb 16 '22 at 11:19

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

2 Answers2