PowerMockito NullPointerException when stub

Question

I want to stub the public static function readAllBytes from java.nio.file.Files with the following test code.

@PrepareForTest(Files.class)
public void testGetNotExistingRestFile() throws Exception {
    PowerMockito.mockStatic(Files.class);
    PowerMockito.doThrow(mock(IOException.class)).when(Files.readAllBytes(any(Path.class)));
}

Every time an NullPointerException is thrown and I can figure out what I'm doing wrong.

java.lang.NullPointerException
at java.nio.file.Files.provider(Files.java:67)
at java.nio.file.Files.newByteChannel(Files.java:317)
at java.nio.file.Files.newByteChannel(Files.java:363)
at java.nio.file.Files.readAllBytes(Files.java:2981)
at nl.mooij.bob.RestFileProviderTest.testGetNotExistingRestFile(RestFileProviderTest.java:53)

How can I stub the function readAllBytes from java.nio.file.Files with PowerMockito?

Are you using [`@PrepareForTest`](http://powermock.googlecode.com/svn-history/r1254/docs/powermock-1.3.5/apidocs/org/powermock/core/classloader/annotations/PrepareForTest.html) ? — khelwood, Apr 11 '15 at 21:27
There's some guidance about mocking static methods here: https://code.google.com/p/powermock/wiki/MockStatic — khelwood, Apr 11 '15 at 21:29
It might not be related to your problem, but is there a reason you throw a mock `IOException` instead of just `doThrow(IOException.class)` ? — khelwood, Apr 11 '15 at 21:38
doThrow (java.lang.Throwable) in PowerMockito cannot be applied to (java.lang.Class ) — bmooij, Apr 11 '15 at 21:46

Jose Tepedino · Answer 1 · 2015-09-18T02:42:21.147

Call Mockito, instead of PowerMockito and reverse the stubbing order:

@Test(expected=IOException.class)
@PrepareForTest(Files.class)
public void testGetNotExistingRestFile() throws Exception {
    // arrange
     PowerMockito.mockStatic(Files.class);
     Mockito.when(Files.readAllBytes(Matchers.any(Path.class))).thenThrow(Mockito.mock(IOException.class));
    // act
     Files.readAllBytes(Mockito.mock(Path.class));
}

Another possibility is:

   @Test(expected=IOException.class)
   @PrepareForTest(Files.class)
   public void testGetNotExistingRestFile() throws Exception {
     // arrange
       PowerMockito.mockStatic(Files.class);
       Files filesMock = PowerMockito.mock(Files.class);
       Mockito.when(filesMock.readAllBytes(Matchers.any(Path.class))).thenThrow(Mockito.mock(IOException.class));
     // act   
       filesMock.readAllBytes(Mockito.mock(Path.class));
   }

Reference: Using PowerMockito to Mock Final and Static Methods

For some reason I had to have `@PrepareForTest(Files.class, ClassThatCallsFiles.class)`, but otherwise it works. — Ben Watson, Feb 12 '18 at 13:56

score 3 · Answer 2 · answered May 23 '17 at 00:22

3

Make sure you are including the class that calls the static method in your @PrepareForTest.

@PrepareForTest({Files.class, ClassThatCallsFiles.class})

answered May 23 '17 at 00:22

nickb

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score 0 · Answer 3 · answered Mar 23 '21 at 11:30

Please add this dependency in pom.xml While Mocking Files class for static method.

<dependency>
    <groupId>org.powermock</groupId>
    <artifactId>powermock-core</artifactId>
    <version>2.0.9</version>
    <scope>test</scope>
</dependency>

This is also one of the factor you are getting NullPointerException

PowerMockito NullPointerException when stub

3 Answers3