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JMockit is a Java toolkit for automated developer testing. It contains APIs for the creation of the objects to be tested, for mocking dependencies, and for faking external APIs; JUnit (4 & 5) and TestNG test runners are supported. It also contains an advanced code coverage tool.
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/*
 * Copyright (c) 2006 Rogério Liesenfeld
 * This file is subject to the terms of the MIT license (see LICENSE.txt).
 */
package mockit;

import java.lang.reflect.*;
import javax.annotation.*;
import static java.lang.reflect.Modifier.*;

import mockit.internal.classGeneration.*;
import mockit.internal.faking.*;
import mockit.internal.reflection.*;
import mockit.internal.startup.*;
import mockit.internal.state.*;
import static mockit.internal.util.GeneratedClasses.*;

/**
 * A base class used in the creation of a fake for an external type, which is usually a class from
 * some library or component used from the internal codebase of the system under test (SUT).
 * Such fake classes can be used as fake implementations for use in unit or integration tests.
 * For example:
 *  * public final class FakeSystem extends MockUp<System> {
 *    @Mock public static long nanoTime() { return 123L; }
 * }
 * 
 * One or more fake methods annotated {@linkplain Mock as such} must be defined in the concrete subclass.
 * Each {@code @Mock} method should have a matching method or constructor in the faked class/interface.
 * At runtime, the execution of a faked method/constructor will get redirected to the corresponding fake method.
 * 
 * When the faked type is an interface, an implementation class is generated where all methods are empty, with non-void
 * methods returning a default value according to the return type: {@code 0} for {@code int}, {@code null} for a
 * reference type, and so on.
 * In this case, an instance of the generated implementation class should be obtained by calling
 * {@link #getMockInstance()}.
 * 

 * When the type to be faked is specified indirectly through a {@linkplain TypeVariable type variable}, there are two
 * other possible outcomes:
 * 

 * If the type variable "extends" two or more interfaces, a fake proxy class that implements all
 * interfaces is created, with the proxy instance made available through a call to {@link #getMockInstance()}.
 * Example:
 *  * @Test
 * public <M extends Runnable & ResultSet> void someTest() {
 *     M fakedInterfaceInstance = new MockUp<M>() {
 *        @Mock void run() { ...do something... }
 *        @Mock boolean next() { return true; }
 *     }.getMockInstance();
 *
 *     fakedInterfaceInstance.run();
 *     assertTrue(fakedInterfaceInstance.next());
 * }
 * 
 * 
 * If the type variable extends a single type (either an interface or a non-final class), then
 * that type is taken as a base type whose concrete implementation classes should also get faked.
 * Example:
 *  * @Test
 * public <BC extends SomeBaseClass> void someTest() {
 *     new MockUp<BC>() {
 *        @Mock int someMethod(int i) { return i + 1; }
 *     };
 *
 *     int i = new AConcreteSubclass().someMethod(1);
 *     assertEquals(2, i);
 * }
 * 
 * 
 * 
 *
 * @param  specifies the type (class, interface, etc.) to be faked; multiple interfaces can be faked by defining a
 * type variable in the test class or test method, and using it as the type argument;
 * if a type variable is used and it extends a single type, then all implementation classes extending or
*  implementing that base type are also faked;
 * if the type argument itself is a parameterized type, then only its raw type is considered
 *
 * @see #MockUp()
 * @see #MockUp(Class)
 * @see #getMockInstance()
 * @see #onTearDown()
 * @see #targetType
 * @see Tutorial
 */
public abstract class MockUp
{
   static { Startup.verifyInitialization(); }

   /**
    * Holds the class or generic type targeted by this fake instance.
    */
   protected final Type targetType;

   @Nullable private final Class fakedClass;
   @Nullable private T fakeInstance;

   /**
    * Applies the {@linkplain Mock fake methods} defined in the concrete subclass to the class or interface specified
    * through the type parameter.
    *
    * @see #MockUp(Class)
    */
   protected MockUp()
   {
      MockUp previousFake = findPreviouslyFakedClassIfFakeAlreadyApplied();

      if (previousFake != null) {
         targetType = previousFake.targetType;
         fakedClass = previousFake.fakedClass;
         return;
      }

      targetType = getTypeToFake();
      Class classToFake = null;

      if (targetType instanceof Class) {
         //noinspection unchecked
         classToFake = (Class) targetType;
      }
      else if (targetType instanceof ParameterizedType) {
         ParameterizedType parameterizedType = (ParameterizedType) targetType;
         //noinspection unchecked
         classToFake = (Class) parameterizedType.getRawType();
      }

      if (classToFake != null) {
         fakedClass = redefineClassOrImplementInterface(classToFake);
      }
      else {
         Type[] typesToFake = ((TypeVariable) targetType).getBounds();

         fakedClass = typesToFake.length > 1 ?
            new FakedImplementationClass(this).createImplementation(typesToFake) :
            new CaptureOfFakedImplementations(this, typesToFake[0]).apply();
      }
   }

   @Nullable
   private MockUp findPreviouslyFakedClassIfFakeAlreadyApplied()
   {
      FakeClasses fakeClasses = TestRun.getFakeClasses();
      MockUp previousFake = fakeClasses.findPreviouslyAppliedFake(this);
      return previousFake;
   }

   @Nonnull
   private Type getTypeToFake()
   {
      Class currentClass = getClass();

      do {
         Type superclass = currentClass.getGenericSuperclass();

         if (superclass instanceof ParameterizedType) {
            return ((ParameterizedType) superclass).getActualTypeArguments()[0];
         }

         if (superclass == MockUp.class) {
            throw new IllegalArgumentException("No target type");
         }

         currentClass = (Class) superclass;
      }
      while (true);
   }

   @Nonnull
   private Class redefineClassOrImplementInterface(@Nonnull Class classToFake)
   {
      if (classToFake.isInterface()) {
         return createInstanceOfFakedImplementationClass(classToFake, targetType);
      }

      Class realClass = classToFake;

      if (isAbstract(classToFake.getModifiers())) {
         classToFake = new ConcreteSubclass(classToFake).generateClass();
      }

      redefineMethods(realClass, classToFake, targetType);
      return classToFake;
   }

   @Nonnull
   private Class createInstanceOfFakedImplementationClass(@Nonnull Class classToFake, @Nullable Type typeToFake)
   {
      FakedImplementationClass fakedImplementationClass = new FakedImplementationClass(this);
      return fakedImplementationClass.createImplementation(classToFake, typeToFake);
   }

   private void redefineMethods(
      @Nonnull Class realClass, @Nonnull Class classToFake, @Nullable Type genericFakedType)
   {
      FakeClassSetup fakeSetup = new FakeClassSetup(realClass, classToFake, genericFakedType, this);
      fakeSetup.redefineMethods();
   }

   /**
    * Applies the {@linkplain Mock fake methods} defined in the fake class to the given class/interface.
    * 
    * In most cases, the constructor with no parameters can be used.
    * This variation should be used only when the type to be faked is not accessible or known from the test code.
    *
    * @see #MockUp()
    */
   protected MockUp(@SuppressWarnings("NullableProblems") Class targetClass)
   {
      targetType = targetClass;
      MockUp previousFake = findPreviouslyFakedClassIfFakeAlreadyApplied();

      if (previousFake != null) {
         fakedClass = previousFake.fakedClass;
         return;
      }

      if (targetClass.isInterface()) {
         //noinspection unchecked
         fakedClass = createInstanceOfFakedImplementationClass((Class) targetClass, targetClass);
      }
      else {
         fakedClass = targetClass;
         //noinspection unchecked
         Class realClass = (Class) targetClass;
         redefineMethods(realClass, realClass, null);
         fakeInstance = null;
      }
   }

   /**
    * Returns the mock instance exclusively associated with this fake instance.
    * If the faked type was an interface, then said instance is the one that was automatically created when the fake was
    * applied.
    * If it was a class, and no such instance is currently associated with this fake object, then a new
    * uninitialized instance of the faked class is created and returned, becoming associated with the fake.
    * 

    * In any case, for a given fake instance this method will always return the same fake instance.
    *
    * @see Tutorial
    */
   public final T getMockInstance()
   {
      if (fakeInstance == null && fakedClass != null) {
         @SuppressWarnings("unchecked") T newInstance = (T) createFakeInstance(fakedClass);
         fakeInstance = newInstance;
      }

      return fakeInstance;
   }

   @Nonnull
   private Object createFakeInstance(@Nonnull Class fakedClass)
   {
      String fakedClassName = fakedClass.getName();

      if (isGeneratedImplementationClass(fakedClassName)) {
         return ConstructorReflection.newInstanceUsingPublicDefaultConstructor(fakedClass);
      }

      if (Proxy.isProxyClass(fakedClass)) {
         return MockInvocationHandler.newMockedInstance(fakedClass);
      }

      return ConstructorReflection.newUninitializedInstance(fakedClass);
   }

   /**
    * An empty method that can be overridden in a fake class that wants to be notified whenever the fake is
    * automatically torn down.
    * Tear down happens when the fake goes out of scope: at the end of the test when applied inside a test, at the end
    * of the test class when applied before the test class, or at the end of the test run when applied through the
    * "fakes" system property.
    * 
    * By default, this method does nothing.
    */
   protected void onTearDown() {}
}