QA/test automation rules

Basic rules for JUnit 4

Rule. Recommend to follow Java code conventions
Rule. Don't miss assertions. One test method should include at least one assertion, otherwise the test will always pass.
Rule. Use assertions with an informative message.
Bad

assertEquals(expected , actual);
assertNull(actual);
assertNotNull(actual);
assertTrue(actual);

.

Good

assertEquals("actual should equals expected", expected , actual);
assertNull("actual should be null", actual);
assertNotNull("actual should not be null", actual);
assertTrue("actual should be true", actual);

Rule. Don't use assertTrue wrongly.
Bad

assertTrue("actual should be same with expected", expected == actual);
assertTrue("actual should equals expected", expected.equals(actual));
assertTrue("actual should be null", actual == null);
assertTrue("actual should not be null", actual != null);

Good

assertSame("actual should be same with expected", expected, actual);
assertEquals("actual should equals expected", expected, actual);
assertNull("actual should be null", actual);
assertNotNull("actual should not be null", actual);

Rule. Use assertArrayEquals instead of assertEquals for array data.
Bad

assertEquals("actual[0] should equals expected0", expected0, actual[0]);
assertEquals("actual[1] should equals expected1", expected1, actual[1]);
assertEquals("actual[2] should equals expected2", expected2, actual[2]);

Good

String[] expected = {"0", "1", "2"};
String[] actual = someMethod();
assertArrayEquals("actual should equals expected", expected, actual);

Rule. Avoid negation in an assertTrue or assertFalse test.
Bad

assertTrue("not empty", !r.isEmpty());

Good

assertFalse("not empty", r.isEmpty());

Rule. Don't catch unexpected exceptions.
Bad

public void testCalculation() {
    try {
        deepThought.calculate();
        assertEquals("Calculation wrong", 42, deepThought.getResult());
    }
    catch(CalculationException ex) {
        Log.error("Calculation caused exception", ex);
    }
}

Good

public void testCalculation() throw CalculationException {
    deepThought.calculate();
    assertEquals("Calculation wrong", 42, deepThought.getResult());
}

Rule. Avoid too complex test. One test should not contain too many asserts. Consider breaking the test scenario into multiple, shorter test scenarios.
Rule. Avoid external dependencies. Others can simply select one test and then run it without extra configurations. e.g. Data file should be placed in the svn with test code, so that newcomers don't need to manually prepare it.
Rule. Don't us random. That makes test uncertain, hard to debug and maintain. Instead of it, prepare enough special test data to cover boundary conditions.
Rule. Name tests properly. "testLoadFileFromServer" is better than "test".
Rule. Clean up in @After/@AfterClass method to avoid affecting other testcases.