Powermock ProcessBuilder constructor with String[].class argument - junit

Question

When I tried to powermock the ProcessBuilder constructor, it successes if the argument is an ArrayList, but it fails when the argument is a String array.
The class to be tested is:
package test;
import java.util.ArrayList;
public class MockProcessBuilder {
public void instance1() throws Exception {
String chmodCmd[] = { "/bin/chmod", "755", "/path/to/dest" + "/" + "file.txt" };
// constructor with String[].class
ProcessBuilder pb = new ProcessBuilder(chmodCmd);
pb.redirectErrorStream(true);
Process proc = pb.start();
proc.waitFor();
}
public void instance2() throws Exception {
ArrayList<String> cmdArrayList = new ArrayList<String>();
cmdArrayList.add("/bin/execScript");
cmdArrayList.add("exec");
cmdArrayList.add("ls -altr");
// constructor with ArrayList.class
ProcessBuilder pb = new ProcessBuilder(cmdArrayList);
pb.redirectErrorStream(true);
Process proc = pb.start();
proc.waitFor();
}
}
The test class is:
package test;
import static org.mockito.Matchers.isA;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.mockito.Mockito;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import java.util.ArrayList;
import java.util.List;
#RunWith(PowerMockRunner.class)
#PrepareForTest({MockProcessBuilder.class, ProcessBuilder.class})
public class MockProcessBuilderTest {
#Mock ProcessBuilder pb;
#Mock Process proc;
// fail. NullPointerException
#Test
public void testInstance1() throws Exception {
PowerMockito.whenNew(ProcessBuilder.class).withParameterTypes(String[].class).withArguments(isA(String[].class)).thenReturn(pb);
Mockito.when(pb.start()).thenReturn(proc);
MockProcessBuilder mpb = new MockProcessBuilder();
mpb.instance1();
}
// success
#Test
public void testInstance2() throws Exception {
PowerMockito.whenNew(ProcessBuilder.class).withParameterTypes(List.class).withArguments(isA(ArrayList.class)).thenReturn(pb);
Mockito.when(pb.start()).thenReturn(proc);
MockProcessBuilder mpb = new MockProcessBuilder();
mpb.instance2();
}
}
The first test case fails with error:
java.lang.NullPointerException
Could anyone know how to mock the first constructor?
Thanks
EDIT
full trace:
java.lang.NullPointerException
at test.MockProcessBuilder.instance1(MockProcessBuilder.java:14)
at test.MockProcessBuilderTest.testInstance1(MockProcessBuilderTest.java:32)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:68)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:310)
at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:88)
at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:96)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:294)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:127)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:82)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:282)
at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:86)
at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:207)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:146)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:120)
at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:33)
at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:45)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:118)
at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:101)
at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:53)
at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:53)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Answer 1

The testInstance1() test is failing because the argument matcher isA(String[].class) doesn't match the String varargs arguments that you're giving. To make the test pass, replace the testInstance1() line
PowerMockito.whenNew(ProcessBuilder.class).withParameterTypes(String[].class).
withArguments(isA(String[].class)).thenReturn(pb);
with
PowerMockito.whenNew(ProcessBuilder.class).withParameterTypes(String[].class).
withArguments(anyVararg()).thenReturn(pb);
Powermock is intercepting the call to the ProcessBuilder varargs constructor due to PowerMockito.whenNew(ProcessBuilder.class).withParameterTypes(String[].class) matching the varargs constructor. However, because withArguments(isA(String[].class)) does not match, the thenReturn gets ignored and Powermock just returns null instead of the pb mock.
See also How to properly match varargs in Mockito