Using JMockit to return the actual instance from the mocked constructor

Question

I considered the following question, and this is not the same as mine:

jMockit: how to expect constructor calls for mocked objects?

This question is similar, but the answer does not help me:

How to make fun of the default constructor of the Date class using JMockit?

I am trying to make moker call the constructor java.util.zip.ZipFile , especially the one that has the java.io.File argument. I would like the constructor to return an instance of another ZipFile , which I will create using a constructor that takes only the String argument.

This constructor call occurs inside the test method, so I cannot insert a ZipFile as a parameter.

For example, the code looks something like this:

 public void whatever() { //some code //some more code foo(); //yet more unrelated code } private Blah foo() { ZipFile zf; //a bunch of code we don't care about zf = new ZipFile(someFile);// I want to give it a known zipfile! mock this! // some more code we don't care about Enumeration<?> entries = zf.entries(); ZipEntry entry = (ZipEntry) entries.nextElement(); InputStream is = zf.getInputStream(entry) //maybe some other calls to the ZipFile // do something else } 

My first thought was to do the following with static partial mockery:

 final ZipFile test = new ZipFile("path/to/actual.zip"); new NonStrictExpectations() { @Mocked("(java.io.File)") ZipFile zf; { new ZipFile((File) any); result = test; } }; 

But this will not work, as indicated in this line in the tutorial: constructors have void return type, so it makes no sense to record return values for them

My second thought was to try the following:

 new NonStrictExpectations() { { newInstance("java.util.zip.ZipFile", new File("path/to/actual.zip")); } }; 

But when you try to initialize the file, this causes the following:

 java.util.zip.ZipException: error in opening zip file at java.util.zip.ZipFile.open(Native Method) at java.util.zip.ZipFile.<init>(Unknown Source) at java.util.zip.ZipFile.<init>(Unknown Source) 

My third thought was to use @MockClass as shown below:

 @Before public void setUp() throws Exception { Mockit.setUpMocks(MockedZipFile.class); } @After public void tearDown() { Mockit.tearDownMocks(); } @MockClass(realClass=ZipFile.class) public static class MockedZipFile { public ZipFile it; @Mock public void $init(File f) throws ZipException, IOException { it = new ZipFile("path/to/actual.zip");//this is what would be called } } 

But these are the hoses for some other layouts that I have, loading the configuration file for another part of my test class. Not to mention that I need different zip files for different test cases.

I suppose I could make fun of everything ZipFile , but it would quickly become a huge pain, because it was called a lot of places, the output would be a mockery, etc. etc. Refactoring to try to make it accessible will be inconvenient, since the code that uses ZipFile is internal to the code, and public methods really don't care about that.

I have a feeling that JMockit allows this to be resolved (by giving a specific instance of the object when the constructor is called), but I cannot figure it out. Does anyone have any ideas?

EDIT: I tried the method suggested by @Rogerio, but I have a new error. Here is my setup:

 final ZipFile test = new ZipFile("path/to/actual.zip"); new NonStrictExpectations() { ZipFile zf; { zf.entries(); result = test.entries(); zf.getInputStream((ZipEntry) any); result = new Delegate() { InputStream getInputStream(ZipEntry entry) throws IOException { return test.getInputStream(entry); } }; } }; 

but I get the following stack trace:

 java.lang.InternalError at path.to.test.ExtractDataTest$1.<init>(ExtractDataTest.java:61) at path.to.test.ExtractDataTest.setUp(ExtractDataTest.java:61) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197) 

where line 61 is the line new NonStrictExpectations() { .

I really want to say, "instead of mocking this object, replace this other object of the same type." Maybe I said it badly.

EDIT2: I figured it should include version numbers: Using Eclipse 3.6.1 Java 1.6.0_26 JMockit 0.999.10

Answer 1

JMockit can mock the ZipFile class, but it interferes with loading classes, since the JarFile subclass JarFile used by the JVM all the time (whenever it loads a class from a jar file in the classpath). There is currently no easy way to avoid this intervention (there is a plan to “fix” it, but it will take time).

However, this specific test case is not suitable for a mocking instrument anyway. Instead, I would recommend setting up the test so that it provides the actual zip file with the right content in the right place.

(another edit) I just applied the change to JMockit (for release 0.999.12), which allows you to pass the following test if there is a test.zip file in the working directory and it contains a text file whose first line is "test":

 @Test public void mockZipFile() throws Exception { final ZipFile testZip = new ZipFile("test.zip"); new NonStrictExpectations() { @Capturing @Injectable ZipFile mock; { mock.entries(); result = testZip.entries(); mock.getInputStream((ZipEntry) any); result = new Delegate() { InputStream delegate(ZipEntry e) throws IOException { return testZip.getInputStream(e); } }; } }; ZipFile zf = new ZipFile("non-existing"); ZipEntry firstEntry = zf.entries().nextElement(); InputStream content = zf.getInputStream(firstEntry); String textContent = new BufferedReader(new InputStreamReader(content)).readLine(); assertEquals("test", textContent); } 

However, I would recommend not using the mocking API for such cases. Use a real file instead.

Answer 2

This probably won't help you, but if you use Mockito or EasyMock, you can add PowerMock, which allows you to mock the construction of new objects in the test code.