Mock a decorated Stream using PowerMockito - io

Question

So I have a class which takes an OutputStream in the constructor and creates a PrintWriter from it inside a method. Question is how do I get this PrintWriter to verify it?
Example public Class(OutputStream output) {}
public void foo() {
PrintWriter writer = new PrintWriter(output);
}
What I try to do is:
PrintWriter writer = PowerMockito.mock(PrintWriter.class)
PowerMockito
.whenNew(PrintWriter.class)
.withArguments(output)
.thenReturn(writer);
However I get that there are no interractions with this writer. Any help would be appreciated.

Answer 1

It will be better if you provided full code snippet with PowerMock configuration. Then I could help you and give advise, now I may only guess what could be wrong, but I'm trying:
The PrintWriterhas several constructors which could accept OutputStreamand PowerMock have a defect that it could incorrect guess which constructor is mocked, when you pass only arguments when a class had overloaded constructors.
Also it could be common mistake, you haven't added the class which create an instance of PrintWriter to #PrepareForTest.
So, worked example in base on my assumption case:
public class PrintWriterCreator {
private final PrintWriter printWriter;
public PrintWriterCreator(OutputStream outputStream) {
this.printWriter = new PrintWriter(outputStream);
}
public void write(String message){
printWriter.write(message);
}
}
Test class:
#RunWith(PowerMockRunner.class)
#PrepareForTest({PrintWriter.class, PrintWriterCreator.class})
public class PrintWriterCreatorTest {
#Mock
private OutputStream outputStream;
#Mock
private PrintWriter printWriterMock;
private PrintWriterCreator printWriterCreator;
#Before
public void setUp() throws Exception {
whenNew(PrintWriter.class).withParameterTypes(OutputStream.class).withArguments(eq(outputStream)).thenReturn
(printWriterMock);
printWriterCreator = new PrintWriterCreator(outputStream);
}
#Test
public void testWrite() throws Exception {
String message = "someMessage";
printWriterCreator.write(message);
verifyNew(PrintWriter.class).withArguments(outputStream);
verify(printWriterMock).write(eq(message));
}
}