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PowerMock won't mock static method to throw an Exception in a Spring-Boot application

I realize there are many many very similar questions. I've been through all of them and I still cannot make my code work.
I have a service defined in my Spring-Boot application, just like this:
#Service
public class FileStorageService {
private final Path fileStorageLocation;
#Autowired
public FileStorageService(final FileStorageProperties fileStorageProperties) {
//FileStorageProperties is a very simple class that right now just holds one String value
this.fileStorageLocation = Paths.get(fileStorageProperties.getUploadDir())
.toAbsolutePath()
.normalize();
try {
Files.createDirectories(fileStorageLocation);
} catch (IOException e) {
// FileStorageException is my custom, runtime exception
throw new FileStorageException("Failed to create directory for stored files", e);
}
}
}
And I want to test scenario, when directory creation fails and thus I need to mock method Files.createDirectories(). My test class looks like this:
import org.junit.Test;
import org.junit.runner.RunWith;
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.io.IOException;
import java.nio.file.Files;
#RunWith(PowerMockRunner.class)
#PrepareForTest({Files.class})
public class FileStorageServiceTest {
private static final String UPLOAD_DIR = "uploadDir";
#Test(expected = FileStorageException.class)
public void some_test() throws IOException {
PowerMockito.mockStatic(Files.class);
PowerMockito.when(Files.createDirectories(Mockito.any())).thenThrow(new IOException());
new FileStorageService(createFileStorageProperties());
}
private FileStorageProperties createFileStorageProperties() {
final FileStorageProperties fileStorageProperties = new FileStorageProperties();
fileStorageProperties.setUploadDir(UPLOAD_DIR);
return fileStorageProperties;
}
}
I believe I followed every step from tutorials and questions I've read.
I use:
#RunWith(PowerMockRunner.class),
#PrepareForTest({Files.class}),
PowerMockito.mockStatic(Files.class),
and PowerMockito.when(Files.createDirectories(Mockito.any())).thenThrow(new IOException());.
Still, no exception is thrown during test and it fails. WIll be super thankful for the help, cause I feel I miss something really simple and just cannot see it.

From: https://github.com/powermock/powermock/wiki/Mock-System
Normally you would prepare the class that contains the static methods (let's call it X) you like to mock but because it's impossible for PowerMock to prepare a system class for testing so another approach has to be taken. So instead of preparing X you prepare the class that calls the static methods in X!
Basically, we mock the class's use of the System class, rather than unmockable System class itself.
#PrepareForTest({Files.class})
An alternative, non-Powermock way to do this without mocking any system class would be to create a helper method, #Spy the original class, and mock that helper method specifically to throw the exception.
when(spy.doSomethingWithSystemClasses()).thenThrow(new Exception("Foo");

Powermock static final method in final class

The Test case I am writing for:
public class AClassUnderTest {
// This test class has a method call
public Long methodUnderTest() {
// Uses the FinalUtilityClass which contains static final method
FinalUtilityClass.myStaticFinalMethod(<3-parameters-here>);
// I want to mock above call so that test case for my "methodUnderTest" passes
}
}
I have one final class.
public final class FinalUtilityClass {
/**
* Method has 3 parameters
*/
public static final MyBean myStaticFinalMethod(<3-parameters-here>) {
}
}
I have already added below code in my test class:
#RunWith(PowerMockRunner.class)
#PrepareForTest({ FinalUtilityClass.class })
I want to write test case for mocking it.
I want to mock the call of myStaticFinalMethod() so that I can get the expected MyBean instatnce which I can use in further code to pass my test case.
The <3-parameters-here> are Calendar, String, String.
I tried doing:
1)
PowerMockito.mock(FinalUtilityClass.class)
PowerMockito.when(FinalUtilityClass.myStaticFinalMethod(<3-parameters-here>).thenReturn(new MyBean());
2)
PowerMockito.mockStatic(FinalUtilityClass.class)
PowerMockito.when(FinalUtilityClass.myStaticFinalMethod(<3-parameters-here>).thenReturn(new MyBean());
3)
PowerMockito.spy(FinalUtilityClass.class)
PowerMockito.when(FinalUtilityClass.myStaticFinalMethod(<3-parameters-here>).thenReturn(new MyBean());
But nothing worked for me. Please suggest what is correct way for mocking static final method in final class.

The following steps are required to mock calls to static methods:
Use the #RunWith(PowerMockRunner.class) annotation at the class-level of the test case.
Use the #PrepareForTest(ClassThatContainsStaticMethod.class) annotation at the class-level of the test case
Use PowerMock.mockStatic(ClassThatContainsStaticMethod.class) to mock all methods of this class
When you follow these steps as documented, your tests should work. And as the OP seems to be confused about PowerMock vs. PowerMockito - that is (more or less) the same thing:
PowerMock and PowerMockito are based on the same technology. They just have different "connectors" to either work with EasyMock or Mockito. So, yes the above example says PowerMock.mockStatic() - but PowerMockito has mockStatic() methods as well. In that sense: the core things (for example regarding preparation with annotations) are the same. See here for example (they are so close that the linked tutorial says "Intro to PowerMock" - although it does introduce PowerMockito.
And as you seem to not believe me - see this example:
package ghostcat.test;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
final class ClassWithStatic {
public final static int ignoreMethodCall(String a, String b, int c) {
System.out.println("SHOULD NOT SHOW UP: " + a);
return c;
}
}
#RunWith(PowerMockRunner.class)
#PrepareForTest(ClassWithStatic.class)
public class MockStaticTest {
#Test
public void test() {
PowerMockito.mockStatic(ClassWithStatic.class);
PowerMockito.when(ClassWithStatic.ignoreMethodCall("a", "b", 5)).thenReturn(42);
org.junit.Assert.assertEquals(ClassWithStatic.ignoreMethodCall("a", "b", 5), 42);
}
}
This test passes; and doesn't print anything. Therefore the final static method gets mocked.

I faced a similar problem, and it cost me a lot of time.
I solved it, based on this Mock system class with PowerMock documentation, when I realized that the #PrepareForTest({ SomeClassToBePreparedForTesting.class }) must receive the class that calls the static methods defined in the final class, so the preparation for the test, in your case, must receive the AClassUnderTest.class.
#RunWith(PowerMockRunner.class)
#PrepareForTest({ AClassUnderTest.class })
The correct way to mock the final class with the target static method is to use the PowerMock.mockStatic(FinalClassThatDefinesStaticMethod.class), in your case the FinalUtilityClass.class.
PowerMockito.mockStatic(FinalUtilityClass.class)
PowerMockito.when(FinalUtilityClass.method(params)).thenReturn(return);
In addition, if you have some issue like: 'It's not possible to mock final methods', you can create the file org/powermock/extensions/configuration.properties and set this config mockito.mock-maker-class=mock-maker-inline like the PowerMockito documentation presents.

Recursively call system while mocking

I've been trying for a while to mock my codes. I'm newby on mocking so lots of things ahead of me to catch. I'm using Powermockito with Mockito and Easymock integration.
I'm having difficulties with mocking a method which is inside the method I wanted to test. So here is an example of the situation I faced:
public class trialClass {
public static int try2(){
return 3;
}
public static int try(int a){
return try2() + a;
}
}
and my test class is:
#RunWith(PowerMockRunner.class)
#PrepareForTest(trial.class)
public class trialTest {
#Before
public void setUp() throws Exception {
PowerMockito.mockStatic(trial.class);
//Here I expect try2() to return 10, even it return 3
PowerMockito.when(trial.try2()).thenReturn(10);
}
#Test
public void testtry() throws Exception {
//After try2() returns 10 recursively inside my try() method,
//I expect result to be 11
Assert.assertEquals(11, trial.try(1));
}
}
This question of mine actually comes from my session variable. My session holds some value and an X method returns that value. All I need is to mock that X method recursively and this question just simulates this case.
Thanks for your help guys.

You need to use Mockito.CALLS_REAL_METHODS
So in your test setup:
PowerMockito.mockStatic(trial.class, CALLS_REAL_METHODS);

EDIT
It occurred to me that you might not want to change to EasyMock instead of Mockito, in that case please disregard...
Partial mocking is the keyword you are after. You don't want to mock everything, just try2(). You should use the PowerMock.mockStaticPartial(Class, String...) method.
Instead of
PowerMockito.mockStatic(trialClass.class);
Use
PowerMock.mockStaticPartial(trialClass.class, "try2");
And then do the actual mocking.
Also note that you defined the clas as trialClass in the code above, but use trial.class in the second code...

Please find an updated version of your TrialTest.java using EasyMock with PowerMock as a solution. PowerMock is easy to configure and does not interfere with most existing jars. You only need a few JARS
powermock-easymock-X.X.X-full.jar
Easymock-X.X.jar
You had some issues with your code that I fixed:
Code Issue: try is a Java keyword so it cannot be used in method name (e.g., try(int a)).
Code Quality: Use Java Object instead of Java primitive (e.g., Use Integer instead of int).
Code Quality: trialClass is a poor Java class name (e.g., Use upperCase for Java class name, don't use the generic word Class unless for educational purposes), maybe Trial.
Here's the updated code:
Trial.java (CUT)
public class Trial {
public static Integer try2() {
return 3;
}
public static Integer try1(int a) {
return try2() + a;
}
}
Working Test Class: TrialTest.java
import org.easymock.EasyMock;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.easymock.PowerMock;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
#RunWith(PowerMockRunner.class)
#PrepareForTest(Trial.class)
public class TrialTest {
#Before
public void setUp() throws Exception {
/* Setup */
PowerMock.mockStaticPartial(Trial.class, "try2");
/* Mocks */
// Here I expect try2() to return 10, even it return 3
EasyMock.expect(Trial.try2()).andReturn(10).atLeastOnce();
PowerMock.replayAll();
}
#Test
public void testtry() throws Exception {
// After try2() returns 10 recursively inside my try() method,
// I expect result to be 11
/* Test */
Integer result = Trial.try1(1);
/* Asserts */
PowerMock.verifyAll();
Assert.assertEquals(new Integer(11), result);
}
}

PowerMock: Mocking static method that affect one test only

My situation:
I would like to add a new test. And I need to mock one static method X of Service class.
Unfortunately existing tests are using this static method in some way.
And when I mock X method using PowerMock then other test failed.
What is more I shouldn't touch other tests.
Is there any opportunity to mock static methods for one test only? ( using PowerMock).
Thanks in advance.

Sure, it is possible! The only time when you could run into problems is if you are trying to test multiple threads at the same time... I put an example of how to do it below. Enjoy.
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.easymock.PowerMock;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
import static org.easymock.EasyMock.*;
import static org.junit.Assert.*;
#RunWith(PowerMockRunner.class)
#PrepareForTest(IdGenerator.class)
public class TestClass {
#Test
public void yourTest()
{
ServiceRegistrator serTestObj = new ServiceRegistrator();
PowerMock.mockStatic(IdGenerator.class);
expect(IdGenerator.generateNewId()).andReturn(42L);
PowerMock.replay(IdGenerator.class);
long actualId = IdGenerator.generateNewId();
PowerMock.verify(IdGenerator.class);
assertEquals(42L,actualId);
}
#Test
public void unaffectedTest() {
long actualId = IdGenerator.generateNewId();
PowerMock.verify(IdGenerator.class);
assertEquals(3L,actualId);
}
}
TestClass
public class IdGenerator {
public static long generateNewId()
{
return 3L;
}
}

The easiest way to solve your problem is create new test class and place your tests there.
You can also wrap up this static class with normal class hidden behind interface in your code and stub this interface in your tests.
Last thing you can try is to stub each method of your static class in #SetUp method using:
Mockito.when(StaticClass.method(param)).thenCallRealMethod();
and stub particular method in your test using:
Mockito.when(Static.methodYouAreInterested(param)).thenReturn(value);

For those looking to achieve this using Mockito with PowerMocks, this can be done by adding the #PrepareForTest annotation to the tests themselves that need to mock out the values instead of the test class itself.
In this example, let's pretend there is SomeClass that has a static function (returnTrue()) that always returns true like so:
public class SomeClass {
public static boolean returnTrue() {
return true;
}
}
This example shows how we can mock out the static call in one test and allow the original functionality to stay the same in another.
#RunWith(PowerMockRunner.class)
#Config(constants = BuildConfig.class)
#PowerMockIgnore({"org.mockito.*", "android.*"})
public class SomeTest {
/** Tests that the value is not mocked out or changed at all. */
#Test
public void testOriginalFunctionalityStays()
assertTrue(SomeClass.returnTrue());
}
/** Tests that mocking out the value works here, and only here. */
#PrepareForTest(SomeClass.class)
#Test
public void testMockedValueWorks() {
PowerMockito.mockStatic(SomeClass.class);
Mockito.when(SomeClass.returnTrue()).thenReturn(false);
assertFalse(SomeClass.returnTrue())
}
}

Mock Runtime.getRuntime()?

Can anyone make any suggestions about how best to use EasyMock to expect a call to Runtime.getRuntime().exec(xxx)?
I could move the call into a method in another class that implements an interface, but would rather not in an ideal world.
interface RuntimeWrapper {
ProcessWrapper execute(String command) throws IOException;
}
interface ProcessWrapper {
int waitFor() throws InterruptedException;
}
I was wondering if anyone had any other suggestions?

Your class shouldn't call Runtime.getRuntime(). it should expect a Runtime to be set as its dependency, and work with it. Then in your test you can easily provide a mock and set it as a dependency.
As a sidenote, I'd suggest watching this lecture on OO Design for testability.
Update: I didn't see the private constructor. You can try using java bytecode instrumentation in order to add another constructor or make the constructor public, but that might turn out to be impossible as well (if there are some restrictions on that class).
So your option is to make a wrapper (as you suggested in the question), and follow the dependency-injection approach.

Bozho above is IMO the Correct Solution. But it is not the only solution. You could use PowerMock or JMockIt.
Using PowerMock:
package playtest;
public class UsesRuntime {
public void run() throws Exception {
Runtime rt = Runtime.getRuntime();
rt.exec("notepad");
}
}
package playtest;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.legacy.PowerMockRunner;
import static org.powermock.api.easymock.PowerMock.*;
import static org.easymock.EasyMock.expect;
#RunWith(PowerMockRunner.class)
#PrepareForTest( { UsesRuntime.class })
public class TestUsesRuntime {
#Test
public void test() throws Exception {
mockStatic(Runtime.class);
Runtime mockedRuntime = createMock(Runtime.class);
expect(Runtime.getRuntime()).andReturn(mockedRuntime);
expect(mockedRuntime.exec("notepad")).andReturn(null);
replay(Runtime.class, mockedRuntime);
UsesRuntime sut = new UsesRuntime();
sut.run();
}
}

Perhaps instead of mocking Runtime.getRuntime().exec() you could "mock" the script/program/etc. it's supposed to be calling.
Instead of passing the real command-line string into exec(), write a test script and execute it instead. You could have the script return hard-coded values you could test against just like a mocked class.

Here is how you would do it with EasyMock 3.0 (and JUnit 4):
import org.junit.*;
import org.easymock.*;
import static org.easymock.EasyMock.*;
public final class EasyMockTest extends EasyMockSupport
{
#Test
public void mockRuntimeExec() throws Exception
{
Runtime r = createNiceMock(Runtime.class);
expect(r.exec("command")).andReturn(null);
replayAll();
// In tested code:
r.exec("command");
verifyAll();
}
}
The only problem with the test above is that the Runtime object needs to be passed to code under test, which prevents it from using Runtime.getRuntime().
With JMockit, on the other hand, the following test can be written, avoiding that problem:
import org.junit.*;
import mockit.*;
public final class JMockitTest
{
#Test
public void mockRuntimeExec() throws Exception
{
final Runtime r = Runtime.getRuntime();
new NonStrictExpectations(r) {{ r.exec("command"); times = 1; }};
// In tested code:
Runtime.getRuntime().exec("command");
}
}