A First Look at Moq 52
This week I’m working with a customer that uses two tools I have not previously used: MBUnit (instead of NUnit, and it is now part of Gallio [sic]) and Moq (by Daniel Cazzulino).
For how I’m using MBUnit, there are no differences (that’s not to say it’s the same as NUnit, I’m just using it that way). However, Moq is a different mocking framework.
While you can do something similar to a record/playback approach, Moq encourages a different approach. Rather than try to describe it, I’ll show a few examples and you can decide for yourself (or you can tell me how I should have done it better).
Background
Given a login service, I want to make sure it follows a set of requirements. The list of requirements I typically use for this example are here: http://schuchert.wikispaces.com/Tdd.Problems.LoggingIn. What follows are tests that are similar to, but not quite consistent with those requirements.When I was working through this example, I was a little exception happy. I was trying to learn how to make certain things happen with the moq. I’ve simply repeated my experiments here, when I use this later on, I’ll approach this problem a bit differently.
Example 1: Logging in successfully
00: [Test]
01: public void WhenUserFoundAndPasswordMatchesUserShouldBeLoggedIn()
02: {
03: var userMock = new Mock<IUser>();
04: userMock.Setup(user => user.PasswordMatches(It.IsAny<string>())).Returns(true);
05:
06: var daoMock = new Mock<IUserDao>();
07: daoMock.Setup(dao => dao.Get(It.IsAny<string>())).Returns(userMock.Object);
08:
09: var service = new UserService(daoMock.Object);
10: service.Login("Brett", "password");
11:
12: userMock.VerifySet(user => user.LoggedIn = true);
13: }| Line 3 | Create a userMock. |
| Line 4 | Using a C# lambad, when a user object is sent the PasswordMatched message with any string object, return true. |
| Line 6 | Create a mock IUserDao. |
| Line 7 | Whenever the Get method is called with any string, return the userMock’s Object property (the actual mock object). |
| Line 9 | Create a user service and inject into it the daoMock’s Object property (the actual dao mock). |
| Line 10 | Send the login message, which should result in the User being logged in. |
| Line 12 | Verify that the LoggedIn property was set to true. |
Notice that rather than setting expectations, line 12 verifies only what I want to verify. It is possible to call Setup more times and then use “VerifyAll” to confirm all the Setup’s were actually used. However, that makes the test more coupled to the underlying implementation. All I care about is that as a result of this configuration of objects, a user was LoggedIn.
By default, mocks are not strict. That is, code may call any methods it wishes on a give mock object. So the default behavior is more like a stub than a mock object. If you call “VerifyAll” on the userMock or the daoMock, then all of the descriptions in the various Setup method invocations need to happen.
Example 2: User not found? Throw an exception
00: [Test]
01: [ExpectedException(typeof(UserDoesNotExistException))]
02: public void WhenUserNotFoundShouldThrowException()
03: {
04: var daoMock = new Mock<IUserDao>();
05: daoMock.Setup(dao => dao.Get(It.IsAny<string>())).Returns((IUser) null);
06:
07: var service = new UserService(daoMock.Object);
08: service.Login("Brett", "password");
09: }| Line 1 | Create an IUserDao mock. |
| Line 5 | When Get is called with any string, return null – that is, never find an object. I think of this as a kind of Saboteur, which is a specific kind of stub. |
| Line 7 | Create a user service and inject the daoMock.Object property, the actual mock. |
| Line 8 | Call the Login method, which should throw an exception for this test to pass. |
Notice that this example includes another non-strict mock. You can call it as often as you wish and there’s no checking on the methods called. However, this stub should force the implementation of the Login method to throw a UserDoesNotExist exception.
Example 3: Throw an Exception if the password does not match
00: [Test]
01: [ExpectedException(typeof(PasswordDoesNotMatchException))]
02: public void WhenLoginAttemptDoesNotMatchPasswordThrowsException()
03: {
04: var userMock = new Mock<IUser>();
05: userMock.Setup(user => user.PasswordMatches(It.IsAny<string>())).Returns(false);
06:
07: var daoMock = new Mock<IUserDao>();
08: daoMock.Setup(dao => dao.Get(It.IsAny<string>())).Returns(userMock.Object);
09:
10: var service = new UserService(daoMock.Object);
11: service.Login("", "");
12: }| Line 4 | Create an IUser mock. |
| Line 5 | Whenever the PasswordMatches method is called with any string, it will return false. All passwords are wrong! |
| Line 7 | Create an IUserDao mock. |
| Line 8 | Whenever Get is called with any string on the IUserDao mock object, return the userMock.Object property (the real mock object). |
| Line 10 | Create a UserService, injecting the daoMock.Object property (the real IUserDao mock). |
| Line 11 | Logging in with any user/password combination should now throw a PasswordDoesNotMatchException. |
Eample 4: Three failed login attempts should cause user account to be revoked.
00: [Test]
01: public void WhenLoginAttemptThreeTimesInARowWithInvalidPasswordUserRevoked()
02: {
03: var userMock = new Mock<IUser>();
04: userMock.Setup(user => user.PasswordMatches(It.IsAny<string>())).Returns(false);
05:
06: var daoMock = new Mock<IUserDao>();
07: daoMock.Setup(dao => dao.Get(It.IsAny<string>())).Returns(userMock.Object);
08:
09: var service = new UserService(daoMock.Object);
10: for (int i = 0; i < 3; ++i)
11: AttempLoginIgnoringException(service, "");
12:
13: userMock.VerifySet(user => user.Revoked = true);
14: }| Lines 3 – 4 | Create an IUser mock (stub or Saboteur really) that will not match any password. |
| Lines 6 – 7 | Create an IUserDao mock (stub) that will return the userMock.Object for all calls to Get with any string. |
| Line 9 | Create a UserService, injecting the IUserDao mock object. |
| Lines 10 – 11 | Attempt to login 3 times, each of which will fail. |
| Line 13 | Verify that the user.Revoked property was set to true on the userMock object. |
Example 5: Failing 2x with one account and then switching to another account and failing again does not revoke account.
00: [Test]
01: public void LoginWrongPassword2XandThenSwitchAccountsWithWrongPassowrdNothingRevoked()
02: {
03: var userMock1 = new Mock<IUser>();
04: userMock1.Setup(user => user.PasswordMatches(It.IsAny<string>())).Returns(false);
05:
06: var userMock2 = new Mock<IUser>(MockBehavior.Strict);
07: userMock2.Setup(user => user.PasswordMatches(It.IsAny<string>())).Returns(false);
08:
09: var daoMock = new Mock<IUserDao>();
10: daoMock.Setup(dao => dao.Get("user1")).Returns(userMock1.Object);
11: daoMock.Setup(dao => dao.Get("user2")).Returns(userMock2.Object);
12:
13: var service = new UserService(daoMock.Object);
14:
15: AttempLoginIgnoringException(service, "user1");
16: AttempLoginIgnoringException(service, "user1");
17: AttempLoginIgnoringException(service, "user2");
18:
19: userMock2.VerifyAll();
20: }| Lines 3 – 4 | Create user mock that will not match any password. |
| Lines 6 – 7 | Ibid, but this is a strict mock. That is, other than PasswordMatches, no other methods/properties should be called/used (we do not want it’s Revoked property to be set or even called). |
| Lines 9 – 11 | Create an IUserDao mock. Whenever Get is called with “user1”, return userMock1.Object. Whenever Get is called with “user2”, return userMock2. Object. |
| Lines 12 | Create the UserService injecting the daoMock.Object. |
| Lines 15 – 16 | Attempt login 2x to account User1, both will fail. |
| Line 17 | Attempt login to account User2, which will also fail, but we do not want the user2 account revoked. |
| Line 19 | Verify all, meaning that only the PasswordMatches method was called on userMock2.Object. If any other methods were called, the test will fail. |
I love Moq and am happy to see it get more exposure; I’d like to clarify some points.
I don’t think Moq has any affiliation with Google other than being hosted on GoogleCode. To my knowledge, Moq is primarily a product of Dan Cazzulino (Kzu).
Also, when Moq first came out in late 2007, the lambda and generics syntax was novel, but now the other popular .NET mocking frameworks (RhinoMocks, TypeMock Isolator) also support it. My point is just that this approach to mocking is feasible in other frameworks; although, I still find Moq to be the most intuitive framework for the TDD/classicist style of mocking.
Hi Bret, thanks for the good overview of Moq. One thing though, you said in your opening paragraph Moq is Google’s .net mocking framework. As far as I know, Google has no affiliation with the Moq project, it was started by Daniel Cazzulino of Clarius Consulting.
Moq is my mocking library of choice; I find it very intuitive. I’m also pleased to see it getting more exposure.
Al/Robin,
Thanks for that! I’ll update the post.
Indeed, calling Moq “Google’s mocking framework” is like calling ASP.NET MVC “Codeplex’s MVC framework”.
Google just happens to be the project hoster, that’s it.
Moq became my mocking library of choice last year. My only irk was that like other open-source projects, they tend to make significant breaking-changes. (I.e. replacing the “Expect” & related methods with “Setup”) Not that I recall seeing any doco / explanation for the change, but then again we were content using v2.6 for quite some time.
Moq seems good. It reminds me of Mockito (a Java framework). I wonder if it was inspired by it.
Steve, we do not make breaking changes ever (on purpose, anyway).
The renaming of Expect to Setup was not breaking. If you had/have existing tests that use the Expect syntax, they continue to compile and run just fine. We just hide the obsoleted members so that new tests/users can start using the new syntax without the clutter of older APIs.
Same with other things we changed. We can always miss a minor thing here and there when moving forward, but we always spend a good chunk of time in public beta to minimize this, incorporating user feedback.
Thanks for choosing Moq!
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