How to run Gradle test when all tests are UP-TO-DATE?

Question

One option would be using the --rerun-tasks flag in the Forcing tasks to execute section. This would rerun all the the test task and all the tasks it depends on.

If you're only interested in rerunning the tests then another option would be to make gradle clean the tests results before executing the tests. This can be done using the cleanTest task.

Some background - the Java plugin defines a clean tasks to each of the other tasks. According to the Tasks documentation:

cleanTaskName - Deletes files created by specified task. cleanJar will delete the JAR file created by the jar task, and cleanTest will delete the test results created by the test task.

Therefore, all you need in order to re-run your tests is to also run the cleanTest task, i.e.:
gradle cleanTest test

Other option would be to add following in your build.gradle:

test.outputs.upToDateWhen {false}

gradle test --rerun-tasks

Specifies that any task optimization is ignored.

Source: https://gradle.org/docs/current/userguide/gradle_command_line.html

This was recently the topic on Gradle's blog post Stop rerunning your tests. The author shows an example using outputs.upToDateWhen { false } and explains why it is wrong:

This doesn’t actually force reruns

What the author of this snippet probably wanted to say is “Always rerun my tests”. That’s not what this snippet does though. It will only mark the task out-of-date, forcing Gradle to recreate the output. But here’s the thing, if the build cache is enabled, Gradle doesn’t need to run the task to recreate the output. It will find an entry in the cache and unpack the result into the test’s output directory.

The same is true for this snippet:

test.dependsOn cleanTest

Gradle will unpack the test results from the build cache after the output has been cleaned, so nothing will be rerun. In short, these snippets are creating a very expensive no-op.

If you’re now thinking “Okay, I’ll deactivate the cache too”, let me tell you why you shouldn’t.

Then, the author goes on to explain why rerunning some tests is a waste of time:

The vast majority of your tests should be deterministic, i.e. given the same inputs they should produce the same result.

In the few cases where you do want to rerun tests where the code has not changed, you should model them as an input. Here are both examples from the blog post that show adding an input so the task will use it during its up-to-date checks.

task randomizedTest(type: Test) {
  systemProperty "random.testing.seed", new Random().nextInt()
}

---

task systemIntegrationTest(type: Test) {
  inputs.property "integration.date", LocalDate.now()
}

I recommend reading the entire blog post.