src/test/java/org/mockito/StaticMockingExperimentTest.java

/*
 * Copyright (c) 2017 Mockito contributors
 * This program is made available under the terms of the MIT License.
 */
package org.mockito;

import org.junit.Before;
import org.junit.Test;
import org.mockito.exceptions.verification.NoInteractionsWanted;
import org.mockito.exceptions.verification.WantedButNotInvoked;
import org.mockito.exceptions.verification.junit.ArgumentsAreDifferent;
import org.mockito.invocation.Invocation;
import org.mockito.invocation.InvocationFactory;
import org.mockito.invocation.MockHandler;
import org.mockitoutil.TestBase;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

import static org.assertj.core.api.Assertions.assertThat;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.fail;
import static org.mockito.Mockito.doReturn;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.verifyNoMoreInteractions;
import static org.mockito.Mockito.when;
import static org.mockito.Mockito.withSettings;

/**
 * This test is an experimental use of Mockito API to simulate static mocking.
 * Other frameworks can use it to build good support for static mocking.
 * Keep in mind that clean code never needs to mock static methods.
 * This test is a documentation how it can be done using current public API of Mockito.
 * This test is not only an experiment it also provides coverage for
 * some of the advanced public API exposed for framework integrators.
 * <p>
 * For more rationale behind this experimental test
 * <a href="https://www.linkedin.com/pulse/mockito-vs-powermock-opinionated-dogmatic-static-mocking-faber">see the article</a>.
 */
public class StaticMockingExperimentTest extends TestBase {

    Foo mock = Mockito.mock(Foo.class);
    MockHandler handler = Mockito.mockingDetails(mock).getMockHandler();
    Method staticMethod;
    InvocationFactory.RealMethodBehavior realMethod = new InvocationFactory.RealMethodBehavior() {
        @Override
        public Object call() throws Throwable {
            return null;
        }
    };

    @Before public void before() throws Throwable {
        staticMethod = Foo.class.getDeclaredMethod("staticMethod", String.class);
    }

    @Test
    public void verify_static_method() throws Throwable {
        //register staticMethod call on mock
        Invocation invocation = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
            "some arg");
        handler.handle(invocation);

        //verify staticMethod on mock
        //Mockito cannot capture static methods so we will simulate this scenario in 3 steps:
        //1. Call standard 'verify' method. Internally, it will add verificationMode to the thread local state.
        //  Effectively, we indicate to Mockito that right now we are about to verify a method call on this mock.
        verify(mock);
        //2. Create the invocation instance using the new public API
        //  Mockito cannot capture static methods but we can create an invocation instance of that static invocation
        Invocation verification = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
            "some arg");
        //3. Make Mockito handle the static method invocation
        //  Mockito will find verification mode in thread local state and will try verify the invocation
        handler.handle(verification);

        //verify zero times, method with different argument
        verify(mock, times(0));
        Invocation differentArg = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
            "different arg");
        handler.handle(differentArg);
    }

    @Test
    public void verification_failure_static_method() throws Throwable {
        //register staticMethod call on mock
        Invocation invocation = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
            "foo");
        handler.handle(invocation);

        //verify staticMethod on mock
        verify(mock);
        Invocation differentArg = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
            "different arg");

        try {
            handler.handle(differentArg);
            fail();
        } catch (ArgumentsAreDifferent e) {}
    }

    @Test
    public void stubbing_static_method() throws Throwable {
        //register staticMethod call on mock
        Invocation invocation = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
            "foo");
        handler.handle(invocation);

        //register stubbing
        when(null).thenReturn("hey");

        //validate stubbed return value
        assertEquals("hey", handler.handle(invocation));
        assertEquals("hey", handler.handle(invocation));

        //default null value is returned if invoked with different argument
        Invocation differentArg = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
            "different arg");
        assertEquals(null, handler.handle(differentArg));
    }

    @Test
    public void do_answer_stubbing_static_method() throws Throwable {
        //register stubbed return value
        doReturn("hey").when(mock);

        //complete stubbing by triggering an invocation that needs to be stubbed
        Invocation invocation = Mockito.framework().getInvocationFactory()
            .createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod, "foo");
        handler.handle(invocation);

        //validate stubbed return value
        assertEquals("hey", handler.handle(invocation));
        assertEquals("hey", handler.handle(invocation));

        //default null value is returned if invoked with different argument
        Invocation differentArg = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
            "different arg");
        assertEquals(null, handler.handle(differentArg));
    }

    @Test
    public void verify_no_more_interactions() throws Throwable {
        //works for now because there are not interactions
        verifyNoMoreInteractions(mock);

        //register staticMethod call on mock
        Invocation invocation = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
            "foo");
        handler.handle(invocation);

        //fails now because we have one static invocation recorded
        try {
            verifyNoMoreInteractions(mock);
            fail();
        } catch (NoInteractionsWanted e) {}
    }

    @Test
    public void stubbing_new() throws Throwable {
        Constructor<Foo> ctr = Foo.class.getConstructor(String.class);
        Method adapter = ConstructorMethodAdapter.class.getDeclaredMethods()[0];

        //stub constructor
        doReturn(new Foo("hey!")).when(mock);
        Invocation constructor = Mockito.framework().getInvocationFactory().createInvocation(
            mock, withSettings().build(Foo.class), adapter, realMethod, ctr, "foo");
        handler.handle(constructor);

        //test stubbing
        Object result = handler.handle(constructor);
        assertEquals("foo:hey!", result.toString());

        //stubbing miss
        Invocation differentArg = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class),
            adapter, realMethod, ctr, "different arg");
        Object result2 = handler.handle(differentArg);
        assertEquals(null, result2);
    }

    @Test
    public void verifying_new() throws Throwable {
        Constructor<Foo> ctr = Foo.class.getConstructor(String.class);
        Method adapter = ConstructorMethodAdapter.class.getDeclaredMethods()[0];

        //invoke constructor
        Invocation constructor = Mockito.framework().getInvocationFactory().createInvocation(
            mock, withSettings().build(Foo.class), adapter, realMethod, ctr, "matching arg");
        handler.handle(constructor);

        //verify successfully
        verify(mock);
        handler.handle(constructor);

        //verification failure
        verify(mock);
        Invocation differentArg = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class),
            adapter, realMethod, ctr, "different arg");
        try {
            handler.handle(differentArg);
            fail();
        } catch (WantedButNotInvoked e) {
            assertThat(e.getMessage())
                .contains("matching arg")
                .contains("different arg");
        }
    }

    static class Foo {

        private final String arg;

        public Foo(String arg) {
            this.arg = arg;
        }

        public static String staticMethod(String arg) {
            return "";
        }

        @Override
        public String toString() {
            return "foo:" + arg;
        }
    }

    /**
     * Adapts constructor to method calls needed to work with Mockito API.
     */
    interface ConstructorMethodAdapter {
        Object construct(Constructor constructor, Object... args);
    }
}