@Test
  public void injectMetricsBadInputTest() {
    RestRequestMetricsTracker requestMetrics = new RestRequestMetricsTracker();
    try {
      requestMetrics.injectMetrics(null);
      fail("There was no exception even though a null RestRequestMetrics was provided as input for injectMetrics()");
    } catch (IllegalArgumentException e) {
      // expected. nothing to do.
    }
  }
Tests reaction of {@link RestRequestMetricsTracker#injectMetrics(RestRequestMetrics)} to bad input.
ambry-api/src/test/java/com/github/ambry/rest/RestRequestMetricsTrackerTest.java