Allow @WarmUp annotation to prevent bleeding of undesired events

[PKJosh]

For my testing purposes, I wish to limit certain IO events and prevent regression against these metrics. Consider the following example:

@Test
@EnableEvent("jdk.FileRead", threshold = 0)
fun `file is buffered no more than 10 times`() {
    operateOnFile(file)
    jfrEvents.awaitEvents()

    val readCount = jfrEvents.filter(JfrEventTypes.FILE_READ).count()
   assertThat(readCount).isAtMost(10)
}

Every FILE_READ event will be counted, including IO triggered by class loading. This is probably desired from jfrunit’s perspective but can make writing tests a bit cumbersome.

Filtering by jfrEvents by class is possible but the test should probably remain agnostic as to where the IO originates, especially when reads are delegated to an external dependency.

This forces a workaround like the following:

@BeforeAll
fun setup() {
    
    operateOnFile(dummyFile)

}

@Test
@EnableEvent("jdk.FileRead", threshold = 0)
fun `file is buffered no more than 10 times`() {
    operateOnFile(file)
    jfrEvents.awaitEvents()
}



@AfterAll
fun doActualAssertions() {
    val readCount = jfrEvents.filter(JfrEventTypes.FILE_READ).count()
   assertThat(readCount).isAtMost(10)

}


The alternative is handling the boilerplate warmup and jfrEvents.reset() calls in the test itself, a process that would be better handled by an annotation (especially once #126 comes to fruition).

[gunnarmorling]

Hey, that's an interesting proposal. Instead of adding a new annotation like @WarmUp, how about we add support for @EnableEvent() to the existing @Before/@BeforeAll annotations? A PR for implementing this (as for #126) would be more than welcome.

[phejl]

Perhaps I'm missing something but can't you just filter events by file path? Something like (writing without IDE so not 100% sure)

val readCount = jfrEvents.filter(JfrEventTypes.FILE_READ.withPath(file.getAbsolutePath())).count()

BTW I think you don't need jfrEvents.awaitEvents() as when you invoke filter or contains the method will await for events implicitly.

[PKJosh]

After this discussion, I definitely did not seek out enough alternative solutions within the API. The withPath filter combined with jfrEvents.reset() definitely gives me everything I need.

Thanks for the help.