I'm practicing JUnit with Mockito, and trying to test a simple static method
class LessSimpleCalculatorImp implements LessSimpleCalculator {
@Override
public int power(int x, int y) {
return (int)Math.pow(x, y); // <-- try to see if Math.pow has been called
}
}
The test case:
@RunWith(MockitoJUnitRunner.class)
public class LessSimpleCalculator_Test {
@Test
public void test_pow() {
try(MockedStatic<Math> mockedMath = Mockito.mockStatic(Math.class);) {
mockedMath.when(() -> Math.pow(3, 2)).thenReturn(9.0);
int result = lessSimpleCalculator.power(3, 2);
assertEquals(9, result);
mockedMath.verify(() -> Math.pow(3, 2), times(1));
}
}
}
And this gives me a StackOverflowError when I do mvn clean test:
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "main"
ChatGPT says that this is because the mocked class calls Math.pow, which is intercepted by the mocked class, which calls the real class again. How do I fix this?
Also I am using Maven for dependency management:
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-junit-jupiter</artifactId>
<version>5.13.0</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.13.2</version>
<scope>test</scope>
</dependency>
Edit: here is the stack trace
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Forking command line: /bin/sh -c cd /home/username/Desktop/jarvis/core_java/jdbc && /usr/lib/jvm/java-18-openjdk-amd64/bin/java -jar /home/username/Desktop/jarvis/core_java/jdbc/target/surefire/surefirebooter12164676474631886113.jar /home/username/Desktop/jarvis/core_java/jdbc/target/surefire/surefire5274553330454463948tmp /home/username/Desktop/jarvis/core_java/jdbc/target/surefire/surefire_015841166298835331040tmp
Running ca.jrvs.exercise.mockito.LessSimpleCalculator_Test
OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended
*** java.lang.instrument ASSERTION FAILED ***: "!errorOutstanding" with message transform method call failed at ./src/java.instrument/share/native/libinstrument/JPLISAgent.c line: 873
*** java.lang.instrument ASSERTION FAILED ***: "!errorOutstanding" with message transform method call failed at ./src/java.instrument/share/native/libinstrument/JPLISAgent.c line: 873
Exception: java.lang.StackOverflowError thrown from the UncaughtExceptionHandler in thread "main"
Results :
Tests run: 0, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.105 s
[INFO] Finished at: 2024-09-19T14:17:59-04:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.12.4:test (default-test) on project jrvs-jdbc-exercise: Execution default-test of goal org.apache.maven.plugins:maven-surefire-plugin:2.12.4:test failed: The forked VM terminated without saying properly goodbye. VM crash or System.exit called ? -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.12.4:test (default-test) on project jrvs-jdbc-exercise: Execution default-test of goal org.apache.maven.plugins:maven-surefire-plugin:2.12.4:test failed: The forked VM terminated without saying properly goodbye. VM crash or System.exit called ?
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:215)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
at jdk.internal.reflect.DirectMethodHandleAccessor.invoke (DirectMethodHandleAccessor.java:104)
at java.lang.reflect.Method.invoke (Method.java:577)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution default-test of goal org.apache.maven.plugins:maven-surefire-plugin:2.12.4:test failed: The forked VM terminated without saying properly goodbye. VM crash or System.exit called ?
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:148)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
at jdk.internal.reflect.DirectMethodHandleAccessor.invoke (DirectMethodHandleAccessor.java:104)
at java.lang.reflect.Method.invoke (Method.java:577)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
Caused by: java.lang.RuntimeException: The forked VM terminated without saying properly goodbye. VM crash or System.exit called ?
at org.apache.maven.plugin.surefire.booterclient.output.ForkClient.close (ForkClient.java:257)
at org.apache.maven.plugin.surefire.booterclient.ForkStarter.fork (ForkStarter.java:301)
at org.apache.maven.plugin.surefire.booterclient.ForkStarter.run (ForkStarter.java:116)
at org.apache.maven.plugin.surefire.AbstractSurefireMojo.executeProvider (AbstractSurefireMojo.java:740)
at org.apache.maven.plugin.surefire.AbstractSurefireMojo.executeAllProviders (AbstractSurefireMojo.java:682)
at org.apache.maven.plugin.surefire.AbstractSurefireMojo.executeAfterPreconditionsChecked (AbstractSurefireMojo.java:648)
at org.apache.maven.plugin.surefire.AbstractSurefireMojo.execute (AbstractSurefireMojo.java:586)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
at jdk.internal.reflect.DirectMethodHandleAccessor.invoke (DirectMethodHandleAccessor.java:104)
at java.lang.reflect.Method.invoke (Method.java:577)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
[ERROR]
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginExecutionException
It seems like this is a known issue in Mockito, and they aren't going to fix it: https://github.com/mockito/mockito/issues/2105
To be honest, mocking Math.pow is arguably a bad approach anyway, because it means your test needs to have intimate knowledge of LessSimpleCalculatorImp's implementation.
In a contract test, you shouldn't care about LessSimpleCalculatorImp's implementation, just about the end result - you already know the result of 3 to the power of 2 should be 9 (you already have it as the expected result in the assertion!), so just test that:
@Test
public void test_pow() {
int result = lessSimpleCalculator.power(3, 2);
assertEquals(9, result);
}
As a side note, looking at your pom.xml, you're mixing JUnit Jupiter and old JUnit 4. You should probably align to one of them:
<dependencies>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter</artifactId>
<version>5.11.0</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-junit-jupiter</artifactId>
<version>5.13.0</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-core</artifactId>
<version>5.13.0</version>
<scope>test</scope>
</dependency>
</dependencies>
Of course with my suggestion you won't need Mockito anyway, but I'm assuming you have other tests that will still need it.