[TINKERPOP-3079] The test `TraversalStrategiesTest#shouldAllowUserManipulationOfGlobalCache` is not idempotent, as it passes in the first run and fails in repeated runs in the same environment.

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.6.7
• Fix Version/s: 4.0.0, 3.6.8, 3.7.3
• Component/s: structure
• Environment: Ubuntu 22.04, Java 17
• Flags: Patch
• Assignee: Stephen Mallette
• Reporter: Kaiyao Ke
• Created: 17/May/24 07:49
• Updated: 17/May/24 13:34
• Resolved: 17/May/24 13:34

Description

1. 1. 1. Brief Description of the Bug

The test `TraversalStrategiesTest#shouldAllowUserManipulationOfGlobalCache` is non-idempotent, as it passes in the first run but fails in the second run in the same environment. The source of the problem is that the initial strategies registration (`StrategyA`, `StrategyB` and `StrategyC`) for the `TestGraph` and ` TestGraphComputer` classes are static (see https://github.com/apache/tinkerpop/blob/66e5a47ffd3976d29bc7797c399b8e11c5ba810e/gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/TraversalStrategiesTest.java#L132 and https://github.com/apache/tinkerpop/blob/66e5a47ffd3976d29bc7797c399b8e11c5ba810e/gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/TraversalStrategiesTest.java#L185). These static blocks will only be called once during class loading.
In the first execution of the test `TraversalStrategiesTest#shouldAllowUserManipulationOfGlobalCache`, `StrategyA` is removed from global strategies(https://github.com/apache/tinkerpop/blob/66e5a47ffd3976d29bc7797c399b8e11c5ba810e/gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/TraversalStrategiesTest.java#L82), and the test does not restore it after execution.
Therefore, in the second execution of the test, `StrategyA` is not present in the global strategies, so assertions like `assertTrue(strategies.getStrategy(StrategyA.class).isPresent())` would fail(https://github.com/apache/tinkerpop/blob/66e5a47ffd3976d29bc7797c399b8e11c5ba810e/gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/TraversalStrategiesTest.java#L77).

A fix is necessary since unit tests shall be self-contained. Idempotent tests help maintain this isolation by ensuring that the state of the system under test is consistent at the beginning of each test, regardless of previous test runs. For example, fixing non-idempotent tests can help proactively avoid state pollution that results in test order dependency (which could hurt regression testing with the use of test selection / prioritization / parallelism.

1. 1. 1. Failure Message in the 2nd Test Run:
         ```
         java.lang.AssertionError:
         at org.junit.Assert.fail(Assert.java:87)
         at org.junit.Assert.assertTrue(Assert.java:42)
         at org.junit.Assert.assertTrue(Assert.java:53)
         at org.apache.tinkerpop.gremlin.process.TraversalStrategiesTest.shouldAllowUserManipulationOfGlobalCache(TraversalStrategiesTest.java:77)
         ```

1. 1. 1. Reproduce

Use the `NIOInspector` plugin that supports rerunning individual tests in the same environment:
```
cd gremlin-core
mvn edu.illinois:NIOInspector:rerun -Dtest=org.apache.tinkerpop.gremlin.process.TraversalStrategiesTest#shouldAllowUserManipulationOfGlobalCache
```

1. 1. 1. Proposed Fix

Handle initial strategies registration in a `setup()` method rather than in static blocks of test classes.