1. Overview
By default, JUnit runs tests using a deterministic, but unpredictable order (MethodSorters.DEFAULT).
In most cases, that behavior is perfectly fine and acceptable; but there’re cases when we need to enforce a specific ordering.
2. Using MethodSorters.DEFAULT
This default strategy compares test methods using their hashcodes. In case of a hash collision, the lexicographical order is used:
@FixMethodOrder(MethodSorters.DEFAULT)
public class DefaultOrderOfExecutionTest {
private static StringBuilder output = new StringBuilder("");
@Test
public void secondTest() {
output.append("b");
}
@Test
public void thirdTest() {
output.append("c");
}
@Test
public void firstTest() {
output.append("a");
}
@AfterClass
public static void assertOutput() {
assertEquals(output.toString(), "cab");
}
}
When we execute the tests in the class above, we will see that they all pass, including assertOutput().
3. Using MethodSorters.JVM
Another ordering strategy is MethodSorters.JVM – this strategy utilizes the natural JVM ordering – which can be different for each run:
@FixMethodOrder(MethodSorters.JVM)
public class JVMOrderOfExecutionTest {
// same as above
}
Each time we execute the tests in this class, we get a different result.
4. Using MethodSorters.NAME_ASCENDING
Finally, this strategy can be used for running test in their lexicographic order:
@FixMethodOrder(MethodSorters.NAME_ASCENDING)
public class NameAscendingOrderOfExecutionTest {
// same as above
@AfterClass
public static void assertOutput() {
assertEquals(output.toString(), "abc");
}
}
Similarly, when we execute the tests in this class, we see that they all pass, including assertOutput(), which confirms the execution order that we set with the annotation.
5. Conclusion
In this quick tutorial, we went through the ways of setting the execution order available in JUnit.
And, as always, the examples used in this article can be found over on GitHub.