JUnit & Powermock: Native Library already loaded in another classloader

问题:

I have some test classes that need to verify that GLFW-functions were called. But when I want to execute all tests in IntelliJ then I get the error:

Native Library lwjgl.dll already loaded in another classloader

I use Powermock to verify that the static methods have been called:

@RunWith(PowerMockRunner.class) @PrepareForTest({GLFW.class}) public class GlfwWindowImplTest {     // ...     @Test     public void update_swapsBufferAndPollsEvents() {         GlfwWindowImpl target = new GlfwWindowImpl(1L);         mockStatic(GLFW.class);          target.update();          verifyStatic();         GLFW.glfwSwapBuffers(1L);         verifyStatic();         GLFW.glfwPollEvents();     } }  @RunWith(PowerMockRunner.class) @PrepareForTest({GLFW.class}) public class GlfwWindowSystemImplTest {     // ...     @Test(expected = GlfwInitializeException.class)     public void initialize_throwsExceptionIfGlfwInitFails() {         GlfwWindowSystemImpl target = new GlfwWindowSystemImpl();         mockStatic(GLFW.class);         when(GLFW.glfwInit()).thenReturn(GL_FALSE);          target.initialize();     } }

回答1:

It may be a bit late to answer this post, but I ran into a similar problem and I was able to solve it with PowerMock. PowerMock has @SuppressStaticInitializationFor that should help you overcome this issue. Section Suppress static initializer in the link below has a nice example about how to do that:

https://github.com/powermock/powermock/wiki/Suppress-Unwanted-Behavior

Basically, in your case, there could be a class that is calling System.loadLibrary("lwjgl"). You need to locate that class. Example:

public class SomeClass {     ...     static {         System.loadLibrary ("lwjgl");     }     ... }

Then in your test class use @SuppressStaticInitializationFor with the fully qualified name of the class:

@SuppressStaticInitializationFor("com.example.SomeClass")

If in case the class doing the loadLibrary call is an inner class, then you need to add $InnerClass to fully qualify the inner class. Example:

public class SomeClass {     ...     public static class SomeInnerClass {         static {             System.loadLibrary ("lwjgl");         }     }     ... }

Then you need to use:

@SuppressStaticInitializationFor("com.example.SomeClass$SomeInnerClass")

回答2:

@PrepareForTest({GLFW.class}) create new ClassLoader and load ammended class in it. I suspect that GLFW load lwjgl library in its static initializer section.

You can try to unload library, but I don't know what consequences it may lead to.

I suggest wrap GLFW and use that wrapper in your applicatin.

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