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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;

/**
 * An empty interface to be used with the {@link Expectations#result} field or the
 * {@code Invocations#with(Delegate)} method, allowing test code
 * to define varying invocation results or argument matching rules, respectively.
 * 
 * When combined with the {@code result} field, a test will typically assign it with an anonymous class object
 * implementing this interface and containing a delegate method:
 * 
 *    new Expectations() {{
 *       mock.doSomething(anyInt, anyString);
 *       result = new Delegate() {
 *          String delegate(int i, String s) {
 *             return i > 0 ? s : "";
 *          }
 *       };
 *    }};
 *
 *    tested.exerciseCodeUnderTest();
 * 
 * The delegate class (either named or anonymous) must contain exactly one non-private instance method to
 * be executed when the mocked method or mocked constructor is invoked; it can contain any number of {@code private}
 * or {@code static} methods, though.
 * The name of the delegate method can be anything.
 * Its parameters, however, should be the same as the parameters of the corresponding mocked method/constructor, or at
 * least be compatible with them.
 * Optionally, the delegate method can have an extra parameter of type {@link Invocation}, provided it appears as the
 * first one.
 * The delegate method is also allowed to have no parameters (without counting the optional {@code Invocation}
 * parameter).
 * 
 * When used with the {@code result} field, the result of a delegate method execution can be any return value compatible
 * with the recorded method's return type, or a thrown error/exception.
 * 

 * When used with the {@code with(Delegate)} method, the delegate method must return a {@code boolean}, being
 * {@code true} for a successfully matched argument or {@code false} otherwise.
 * 
 * Finally, note that a {@code static} method in the mocked type can have a delegate as well.
 * The same is true for {@code private}, {@code final}, and {@code native} methods.
 *
 * @see Tutorial
 *
 * @param  the type of the argument to be matched, when used with the {@code with(Delegate)} method
 */
public interface Delegate
{
}