I have a Maven project with the following expected results when tests are executed (mvn test):
Tests run: 543, Failures: 0, Errors: 0, Skipped: 8
I was exploring the benefit of running these tests in parallel to see if I could reduce the total elapsed time of the building process.
After adding the following setting to Surefire:
<parallel>methods</parallel>
<threadCount>5</threadCount>
<perCoreThreadCount>true</perCoreThreadCount>
<forkCount>3C</forkCount>
<reuseFork>true</reuseFork>
the number of Skipped tests vary. See the summary below for 50 executions:
01. Tests run: 543, Failures: 2, Errors: 176, Skipped: 8
... 34 runs with similar outputs...
35. Tests run: 543, Failures: 6, Errors: 173, Skipped: 8
36. **Tests run: 543, Failures: 2, Errors: 182, Skipped: 11**
37. **Tests run: 543, Failures: 2, Errors: 176, Skipped: 12**
38. Tests run: 543, Failures: 4, Errors: 177, Skipped: 8
39. Tests run: 543, Failures: 3, Errors: 175, Skipped: 8
40. Tests run: 543, Failures: 4, Errors: 174, Skipped: 8
41. Tests run: 543, Failures: 3, Errors: 172, Skipped: 8
42. Tests run: 543, Failures: 3, Errors: 172, Skipped: 8
43. **Tests run: 543, Failures: 2, Errors: 176, Skipped: 12**
44. Tests run: 543, Failures: 3, Errors: 176, Skipped: 8
... 5 runs with similar outputs...
50. Tests run: 543, Failures: 3, Errors: 172, Skipped: 8
Although it happened in 3/50 of the cases, I was expecting to see different numbers only in Errors and Failures but never in Skipped.
Any thoughts about the subject? Thanks in advance.
EDIT:
FINDING:
Tests can be ignored in runtime execution:
Indeed, there are tests with Assumptions in this particular test suite:
Assume.assumeTrue(InetAddress.getAllByName(host).length > 1);
Assume.assumeNoException(x);
Assume.assumeTrue(sslContextFactory == null);
Assume.assumeNoException(x);
Assume.assumeTrue(OS.IS_LINUX);
Assume.assumeTrue(OS.IS_LINUX);
Assume.assumeTrue(!OS.IS_WINDOWS);
Assume.assumeTrue(!OS.IS_WINDOWS);
Assume.assumeThat(Integer.parseInt(nano), Matchers.greaterThan(21));
Assume.assumeTrue(false);
Assume.assumeTrue(true);
Assume.assumeTrue(false);
Given the circumstances, I believe the non-determinism is due to Assumptions that can be violated when running tests in parallel.