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I'm trying to mock a static method with Mockito

public class UtilsClass {
    public static void sendMessage(
        String to[],
        String subject,
        String body,
        String from,
        String files[])
        throws MessagingException {...}
}

I tried to mock this static method using Mockito.

MockedStatic<UtilsClass> javaMailMockedStatic = org.mockito.Mockito.mockStatic(UtilsClass.class);
javaMailMockedStatic.when(() -> UtilsClass.sendMessage(
        any(String[].class),
        anyString(),
        anyString(),
        anyString(),
        any(String[].class)
    )).then(invocation -> null);

But I keep getting a InvalidUseOfMatchersException

org.mockito.exceptions.misusing.InvalidUseOfMatchersException: 
Misplaced or misused argument matcher detected here:

-> at com.foo.bar.testing.BaseTestCase.lambda$1(BaseTestCase.java:127)
-> at com.foo.bar.testing.BaseTestCase.lambda$1(BaseTestCase.java:128)
-> at com.foo.bar.testing.BaseTestCase.lambda$1(BaseTestCase.java:129)
-> at com.foo.bar.testing.BaseTestCase.lambda$1(BaseTestCase.java:130)
-> at com.foo.bar.testing.BaseTestCase.lambda$1(BaseTestCase.java:131)

You cannot use argument matchers outside of verification or stubbing.
Examples of correct usage of argument matchers:
    when(mock.get(anyInt())).thenReturn(null);
    doThrow(new RuntimeException()).when(mock).someVoidMethod(any());
    verify(mock).someMethod(contains("foo"))

This message may appear after an NullPointerException if the last matcher is returning an object 
like any() but the stubbed method signature expect a primitive argument, in this case,
use primitive alternatives.
    when(mock.get(any())); // bad use, will raise NPE
    when(mock.get(anyInt())); // correct usage use

Also, this error might show up because you use argument matchers with methods that cannot be mocked.
Following methods *cannot* be stubbed/verified: final/private/equals()/hashCode().
Mocking methods declared on non-public parent classes is not supported.

    at com.foo.bar.testing.BaseTestCase.mockMailClasses(BaseTestCase.java:126)
    at com.foo.bar.testing.BaseTestCase.baseSetUp(BaseTestCase.java:70)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:725)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
    at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptLifecycleMethod(TimeoutExtension.java:126)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptBeforeEachMethod(TimeoutExtension.java:76)
    at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.invokeMethodInExtensionContext(ClassBasedTestDescriptor.java:506)
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$synthesizeBeforeEachMethodAdapter$21(ClassBasedTestDescriptor.java:491)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeBeforeEachMethods$3(TestMethodTestDescriptor.java:171)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeBeforeMethodsOrCallbacksUntilExceptionOccurs$6(TestMethodTestDescriptor.java:199)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeBeforeMethodsOrCallbacksUntilExceptionOccurs(TestMethodTestDescriptor.java:199)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeBeforeEachMethods(TestMethodTestDescriptor.java:168)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:131)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:66)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:151)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at java.util.ArrayList.forEach(Unknown Source)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at java.util.ArrayList.forEach(Unknown Source)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:107)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:114)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:95)
    at org.junit.platform.launcher.core.DefaultLauncherSession$DelegatingLauncher.execute(DefaultLauncherSession.java:91)
    at org.junit.platform.launcher.core.SessionPerRequestLauncher.execute(SessionPerRequestLauncher.java:60)
    at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:89)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)

I'm sure that anyString() is the right way to match a string, and that any(ClassName.class) is the correct way to mock any object of type ClassName. It's not working when I use it with a class of type String[].

I don't want to use the general matcher any() since I have different overloads and overrides for the same method that should return different data when mocked.

What is the proper way to mock an array of String in Mockito?

Improve this question
3
  • anyString() and all those others ... are no longer required since ages. Just use any() . The compiler is smart enough these days to infer the required types. Commented Mar 14, 2022 at 9:25
  • 1
    The problem you have is that you're trying to use stubs outside of a verification. You're basically calling a static method (inside lambda) with the any*** methods. Commented Mar 14, 2022 at 9:33
  • @GhostCat What if I have two methods foo(String p) and foo(String[] p). In this case I need to use matchers like anyString so I can set different behaviors for different foo implementations. Right? Commented Mar 14, 2022 at 11:19

1 Answer 1

Reset to default
2

Try changing this:

javaMailMockedStatic.when(() -> JavaMail.postMail(
        any(String[].class),
        anyString(),
        anyString(),
        anyString(),
        any(String[].class)
    )).then(invocation -> null);

into this

verify(
    javaMailMockedStatic.postMail(
        any(String[].class),
        anyString(),
        anyString(),
        anyString(),
        any(String[].class)
    )
);

and see if it still complains. Maybe you won't have to mock the actual postMain implementation, but if you do that's just one more step.

Please paste the whole test so i can figure out the context of what you're trying to do, because you might also need to invoke the method yourself (if it's not invoked from any code paths) with something like

javaMailMockedStatic.postMail( {abc, xyz}, "abc", "cvb", "fdsf", { "dasd" } );

EDIT: Samples if your code is invoking JavaMail directly:

private JavaMail testInstance;

@VisibleInTesting(otherwise = NONE)
public static void setTestInstance(JavaMail newInstance) {
    testInstance = newInstance;
}

// Then, in methods that invoke the JavaMail directly do this:
void methodBeingTested(...) {
  // code
  . . .
  if (testInstance != null) {
     testInstance.postMail ( . . . );
  } else {
     JavaMail.postMail ( . . . );
  }

and you'll have to make a similar hack for everywhere where you invoke javamail directly.

So to avoid making similar hacks everywhere, decouple the JavaMail.

JavaMail can use an instance to perform the actual posting/sending of the message. Which you'll then just replace with a mocked stub in tests and use production code in production. (with the identical piece of code from above)

You should also be able to cover the production version of the JavaMailSender with tests, and put the TestJavaMailSender (which is a mock) in tests.

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1 Comment

However, if your code is invoking JavaMail directly, then you'll need a method for testing, to give it an instance on which to call the method. That makes tests a bit less clean but it is what it is.

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