Fuzzer doesn’t repeat same modifications multiple times

[IlyaMuravjov]

Description (abstract example)

When using Seed.Recursive with modification X, fuzzer doesn't attempt to apply modification X more than once.

Real world (concrete) example

To cover last line of OwnerController#processFindForm method in spring-petclinic project we need to apply orderRepository.save(Owner) modification twice in order to make both ownersResults.isEmpty() and ownersResults.getTotalElements() conditions fail.

To Reproduce

Run the following unit test.

@Test
fun `fuzzer can generate value without two repeated mutations`() {
    runBlocking {
        var seenRepeated = false
        withTimeout(1000) {
            runFuzzing(
                { _, _ -> sequenceOf(Seed.Recursive<Unit, StringBuilder>(
                    construct = Routine.Create(emptyList()) { StringBuilder("") },
                    modify = sequenceOf(Routine.Call(emptyList()) { s, _ -> s.append("1") }),
                    empty = Routine.Empty { fail("Empty is called despite construct requiring no args") }
                )) },
                Description(listOf(Unit))
            ) { _, (s) ->
                if (s.length >= 2) {
                    seenRepeated = true
                    BaseFeedback(Unit, Control.STOP)
                } else BaseFeedback(Unit, Control.CONTINUE)
            }
        }
        Assertions.assertTrue(seenRepeated) { "Unmodified empty string wasn't generated" }
    }
}

Expected behavior

Test passes.

Actual behavior

Test fails.

Visual proofs (screenshots, logs, images)

Timed out waiting for 1000 ms
kotlinx.coroutines.TimeoutCancellationException: Timed out waiting for 1000 ms
	(Coroutine boundary)
	at org.utbot.fuzzing.FuzzingApi.fuzz(Api.kt:352)
	at org.utbot.fuzzing.FuzzerSmokeTest$fuzzer can generate value without two repeated mutations$1$1.invokeSuspend(FuzzerSmokeTest.kt:291)
	at org.utbot.fuzzing.FuzzerSmokeTest$fuzzer can generate value without two repeated mutations$1.invokeSuspend(FuzzerSmokeTest.kt:290)
Caused by: kotlinx.coroutines.TimeoutCancellationException: Timed out waiting for 1000 ms
	at app//kotlinx.coroutines.TimeoutKt.TimeoutCancellationException(Timeout.kt:184)
	at app//kotlinx.coroutines.TimeoutCoroutine.run(Timeout.kt:154)
	at app//kotlinx.coroutines.EventLoopImplBase$DelayedRunnableTask.run(EventLoop.common.kt:508)
	at app//kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:284)
	at app//kotlinx.coroutines.DefaultExecutor.run(DefaultExecutor.kt:108)
	at java.base@17.0.7/java.lang.Thread.run(Thread.java:833)

[alisevych]

@IlyaMuravjov
Seems that two and more Owners saved with the same lastName will satisfy this case too.
Does Fuzzing manage to call save(Owner) several times with different Owners?

[IlyaMuravjov]

@alisevych
No, it calls save method at most once. When I said "repeat same modification" I meant calling same method multiple times (not necessarily with same arguments).

Unit test shows that fuzzer when given a Routine.Create that creates StringBuilder("") and Routine.Call that appends "1" to the StringBuilder is unable to create any StringBuilder that contains at least two characters.