Got flaky tests? Shampoo them away with a quick JUnit rule. Apache 2.

ShampooRule.java

import org.junit.rules.TestRule;
import org.junit.runner.Description;
import org.junit.runners.model.Statement;

/** Got flaky tests? Shampoo them away. */
public final class ShampooRule implements TestRule {
  private final int iterations;

  public ShampooRule(int iterations) {
    if (iterations < 1) throw new IllegalArgumentException("iterations < 1: " + iterations);
    this.iterations = iterations;
  }

  @Override public Statement apply(final Statement base, Description description) {
    return new Statement() {
      @Override public void evaluate() throws Throwable {
        for (int i = 0; i < iterations; i++) {
          base.evaluate();
        }
      }
    };
  }
}

Usage:

@Rule public final TestRule shampoo = new ShampooRule(1000);

Nice work man. 👍

Won't this run the test multiple times, even if it succeeds the first time?

This should fix that:

for (int i = 1; i <= iterations; i++) {
  try {
    base.evaluate();
    break;
  } catch (Throwable e) {
    if (i == iterations) {
      throw e;
    }
  }
}

Or maybe I'm thinking of this rule's purpose a bit differently...

Won't this run the test multiple times, even if it succeeds the first time?
Yes, but that is exactly what this rule is meant for: to run a test x (iterations) number of times to make sure it is a stable test.

Won't this run the test multiple times, even if it succeeds the first time?

Yes, but that is exactly what this rule is meant for: to run a test x (iterations) number of times to make sure it is a stable test.

@JakeWharton-- Mind putting a license block on this? It's pretty useful but probably ought to have an unambiguous statement of license.

Hey man,

I appreciate you posting this. I took it a step further and made a @retries annotation you can add to your test methods directly.

Example:

@test
@retries(3)
public void someTestMethod() {

}

Works with Android custom test runner. Thought it might help anybody who also happens along here. Link:

https://gist.github.com/patrickjh/a65505d53e25e5816b31bb44cbb0e492

Hope that helps someone who comes across this post like I did!