## Why is this an issue?

JUnit assertions should not be made from the `run` method of a `Runnable`, because their failure may not be detected in the test that initiated them. Failed assertions throw assertion errors. However, if the error is thrown from another thread than the one that initiated the test, the thread will exit but the test will not fail.

## How to fix it

Assertions in `Runnable` tasks should be extracted or executed by the main thread to make the whole test fail.

### Code examples

#### Noncompliant code example

    class RunnableWithAnAssertion extends Thread {
      @Override
      public void run() {
        Assert.assertEquals(expected, actual);  // Noncompliant
      }

      @Test
      void test() {
        RunnableWithAnAssertion otherThread = new RunnableWithAnAssertion();
        otherThread.start(); // The assertion in the run method above will be executed by other thread than the current one
        // ...
        // Perform some actions that do not make the test fail
        // ...
        Assert.assertTrue(true);
      }
    }

#### Compliant solution

    class RunnableWithAnAssertion extends Thread {
      @Override
      public void run() {
        Assert.assertEquals(expected, actual);  // Noncompliant
      }

      @Test
      void test() {
        RunnableWithAnAssertion otherThread = new RunnableWithAnAssertion();
        otherThread.run();
        // ...
        // The failed assertions in the run method will prevent us from reaching the assertion below
        // ...
        Assert.assertTrue(true);
      }
    }