Unit tests

Java Transforms supports running unit tests as part of CI checks.

The unit testing environment is set up by default when you apply com.palantir.transforms.lang.java-defaults plugin to your Java transforms subproject. It adds popular Java unit testing libraries JUnit ↗, Mockito ↗ and AssertJ ↗ to the subproject’s testCompile configuration. You should put your test files under src/test/java for Gradle to automatically pick them up. See the steps in Python Tests for more details on how to add plugins to your environment.

Testing with Spark

We provide a JUnit5 extension and a JUnit4 rule to help you easily access a managed SparkSession.

If you are using JUnit5, declare the extension like you would with any regular extension:

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import com.palantir.transforms.lang.java.testing.api.SparkSessionExtension;
import org.junit.jupiter.api.extension.RegisterExtension;

@RegisterExtension
public static SparkSessionExtension sparkSession = new SparkSessionExtension();

If you are on JUnit4 (now deprecated), you can declare the SparkSession in your test files as either a ClassRule or a Rule. For example:

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import com.palantir.transforms.lang.java.testing.api.SparkSessionResource;
import org.junit.ClassRule;

@ClassRule
public static SparkSessionResource sparkSession = new SparkSessionResource();

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import com.palantir.transforms.lang.java.testing.api.SparkSessionResource;
import org.junit.Rule;

@Rule
public static SparkSessionResource sparkSession = new SparkSessionResource();

In both cases, you can then use the extension or rule in your tests normally as shown in the following snippet:

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@Test
public void myUnitTest() {
    SparkSession sparkSession = sparkSession.get();
}

Note that in JUnit4 ClassRule and Rule are different: If you declare the SparkSession as a ClassRule, the same SparkSession will be shared across all the tests inside the test class. This will save you some time on the recreation of SparkSession, but the classpath will be inherited from previously-run tests. By contrast, if you declare the SparkSession as a Rule, you will get a new isolated SparkSession for each individual test. This can cause significant performance degradation if you have many tests using SparkSession in one class.