Using Expectations (or StrictExpectations)
Using a combination of Expectations and Deencapsulation.invoke(), you can partially mock the tested object:
import org.junit.Test;
import static mockit.Deencapsulation.*;
import mockit.*;
public class TestAClass
{
public static class ClassToTest
{
public void methodToTest()
{
boolean returnValue = methodToMock(0);
System.out.println("methodToMock returned " + returnValue);
}
private boolean methodToMock(int value) { return true; }
}
@Tested ClassToTest classToTestInstance;
@Test
public void partiallyMockTestedClass() {
new Expectations(classToTestInstance) {{
invoke(classToTestInstance, "methodToMock", anyInt);
result = false;
times = 2;
}};
classToTestInstance.methodToTest();
classToTestInstance.methodToTest();
classToTestInstance.methodToTest();
}
}
The test above prints:
methodToMock returned false
methodToMock returned false
methodToMock returned true
In general, of course, we should avoid mocking private
methods. That said, I have found in practice that it is sometimes useful to do so, typically when you have a private method which does something non-trivial and was already tested by another test; in such a case, mocking that private method in a second test (either for a different public method or a different path through the same public method) may be significantly easier than setting up necessary inputs/conditions.
Using NonStrictExpectations (deprecated in JMockit 1.23)
It's just as easy to write the test with a NonStrictExpectations (the original attempt by the OP didn't work only because the same non-strict expectation was recorded twice, with the second recording overriding the first):
@Test
public void partiallyMockTestedClass() {
new NonStrictExpectations(classToTestInstance) {{
invoke(classToTestInstance, "methodToMock", anyInt);
returns(false, false, true);
}};
classToTestInstance.methodToTest();
classToTestInstance.methodToTest();
classToTestInstance.methodToTest();
}
Use a Delegate
If more flexibility is needed, we can always record a Delegate
-based result:
@Test
public void partiallyMockTestedClass() {
new NonStrictExpectations(classToTestInstance) {{
invoke(classToTestInstance, "methodToMock", anyInt);
result = new Delegate() {
boolean delegate() {
boolean nextValue = ...choose next return value somehow...
return nextValue;
}
}
}};
classToTestInstance.methodToTest();
classToTestInstance.methodToTest();
classToTestInstance.methodToTest();
}
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