[GitHub] [drill] paul-rogers commented on pull request #2275: DRILL-7972: ClassCastException when joining RDBMS and Elasticsearch tables

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paul-rogers commented on pull request #2275:
URL: https://github.com/apache/drill/pull/2275#issuecomment-882132363


   @vvysotskyi, as it turns out, it is easy to create a "dummy" plugin for such cases. In fact, we have some. The "Mock" storage plugin (which is actually rather complex, because it also generates data). Another is this [super simple](https://github.com/apache/drill/blob/master/exec/java-exec/src/test/java/org/apache/drill/exec/store/BasePluginRegistryTest.java#L116) one.
   
   What you may mean is that we don't have multiple plugins which we can use in an exec unit test, that need the rules which you are modifying. This does, indeed, make this kind of problem very hard to debug, and very hard to test. It also makes it very hard for anyone in the future to avoid breaking things.
   
   Drill does not have "integration" tests, but it could: tests that are run after all plugins are created so the tests have visibility to the entire system. Presumably each plugin has some way to test itself (creates a test DB or whatever.) So, the integration test could use these features to set up two plugins. Very heavy-weight, and very hard to debug (still have to build everything.)
   
   Point is: we do want to have tests so that people can confidently modify the code knowing that tests will catch any mistakes. How can we test fixes such as this?


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