I often face the problem that mock objects need to be brought in a certain state before the "interesting" part of a test can start.
For example, let's say I want to test the following class:
struct ToTest
{
virtual void onEnable();
virtual void doAction();
};
Therefore, I create the following mock class:
struct Mock : ToTest
{
MOCK_METHOD0(onEnable, void());
MOCK_METHOD0(doAction, void());
};
The first test is that onEnable is called when the system that uses a ToTest object is enabled:
TEST(SomeTest, OnEnable)
{
Mock mock;
// register mock somehow
// interesting part of the test
EXPECT_CALL(mock, onEnable());
EnableSystem();
}
So far, so good. The second test is that doAction is called when the system performs an action and is enabled. Therefore, the system should be enabled before the interesting part of the test can start:
TEST(SomeTest, DoActionWhenEnabled)
{
Mock mock;
// register mock somehow
// initialize system
EnableSystem();
// interesting part of the test
EXPECT_CALL(mock, doAction());
DoSomeAction();
}
This works but gives an annoying warning about an uninteresting call to onEnable. There seem to be two common fixes of this problem:
Using NiceMock<Mock> to suppress all such warnings; and
Add an EXPECT_CALL(mock, onEnable()) statement.
I don't want to use the first method since there might be other uninteresting calls that really should not happen. I also don't like the second method since I already tested (in the first test) that onEnable is called when the system is enabled; hence, I don't want to repeat that expectation in all tests that work on enabled systems.
What I would like to be able to do is say that all mock calls up to a certain point should be completely ignored. In this example, I want expectations to be only checked starting from the "interesting part of the test" comment.
Is there a way to accomplish this using Google Mock?
The annoying thing is that the necessary functions are there: gmock/gmock-spec-builders.h defines Mock::AllowUninterestingCalls and others to control the generation of warnings for a specific mock object. Using these functions, it should be possible to temporarily disable warnings about uninteresting calls.
That catch is, however, that these functions are private. The good thing is that class Mock has some template friends (e.g., NiceMock) that can be abused. So I created the following workaround:
namespace testing
{
// HACK: NiceMock<> is a friend of Mock so we specialize it here to a type that
// is never used to be able to temporarily make a mock nice. If this feature
// would just be supported, we wouldn't need this hack...
template<>
struct NiceMock<void>
{
static void allow(const void* mock)
{
Mock::AllowUninterestingCalls(mock);
}
static void warn(const void* mock)
{
Mock::WarnUninterestingCalls(mock);
}
static void fail(const void* mock)
{
Mock::FailUninterestingCalls(mock);
}
};
typedef NiceMock<void> UninterestingCalls;
}
This lets me access the private functions through the UninterestingCalls typedef.
The flexibility you're looking for is not possible in gmock, by design. From the gmock Cookbook (emphasis mine):
[...] you should be very cautious about when to use naggy or strict mocks, as they tend to make tests more brittle and harder to maintain. When you refactor your code without changing its externally visible behavior, ideally you should't need to update any tests. If your code interacts with a naggy mock, however, you may start to get spammed with warnings as the result of your change. Worse, if your code interacts with a strict mock, your tests may start to fail and you'll be forced to fix them. Our general recommendation is to use nice mocks (not yet the default) most of the time, use naggy mocks (the current default) when developing or debugging tests, and use strict mocks only as the last resort.
Unfortunately, this is an issue that we, and many other developers, have encountered. In his book, Modern C++ Programming with Test-Driven Development, Jeff Langr writes (Chapter 5, on Test Doubles):
What about the test design? We split one test into two when we changed from a hand-rolled mock solution to one using Google Mock. If we expressed everything in a single test, that one test could set up the expectations to cover all three significant events. That’s an easy fix, but we’d end up with a cluttered test.
[...]
By using NiceMock, we take on a small risk. If the code later somehow changes to invoke another method on the [...] interface, our tests aren’t going to know about it. You should use NiceMock when you need it, not habitually. Seek to fix your design if you seem to require it often.
You might be better off using a different mock class for your second test.
class MockOnAction : public ToTest {
// This is a non-mocked function that does nothing
virtual void onEnable() {}
// Mocked function
MOCK_METHOD0(doAction, void());
}
In order for this test to work, you can have onEnable do nothing (as shown above). Or it can do something special like calling the base class or doing some other logic.
virtual void onEnable() {
// You could call the base class version of this function
ToTest::onEnable();
// or hardcode some other logic
// isEnabled = true;
}
Related
If i need to test if a method within class under test has been called or not, can it be done without Mockito (or any mocking tool for that matter)?
Reason asking is that wherever i read about Mockito and similar tools, it says one should never mock CUT but its dependencies (that part is clear).
So, if thats the case then there are only 2 options left:
there is some other way of testing it without mocking
or
the fact the method was called should not be tested itself but some side effect or methods return value
For example (trivial and non-realworld), class MyClass can have 2 methods: A() and B(). A conditionay calls B based on some internal state.
After arranging state & acting by calling A() we want to assert that B() was called.
Either its not possible without mocking the whole CUT or 2 methods like this in a single class are always SRP violation smell and call for redesign where B() should actually be (mocked) dependency of MyClass CUT.
So, whats correct?
Usually I tend to not even use spies, instead I prefer to write my code in a way that for any class I write:
I test only non-private methods, since they're entry points into the class under test. So, in your example, if a() calls b(), maybe b() should be be private and, as a consequence, should not be tested. To generalize, a() is something that a class "can do" (a behavior), so I test the behavior, and not the method itself. If this behavior internally calls other things - well, its an internal matter of that class, if possible I don't make any assumptions on how does the class work internally, and always prefer "white-box" testing.
I only test "one" non-private method in a test.
All the methods should return something (best option) or at least call dependencies, or change internal state of the object under test. The list of dependencies is always clean-to-understand, I can't instantiate the object of CUT without supplying it a list of dependencies. For example, using constructor dependency injection is a good way of doing this. I mock only dependencies indeed, and never mock / spy CUT. Dependencies are never static but injected.
Now with these simple rules, the need to "test if a method within class under test has been called or not" basically can boil down to one of the following:
you're talking about private method. In this case - don't test it, test only public things.
The method is public - in this case you explicitly call it in unit test, so its irrelevant.
Now lets ask why do you want to test this if a method within CUT has been called or not?
If you want to make sure that it changed something. If this "something" is within the class - in other words, its internal state has changed, check in test that the change is indeed done in the state by calling another method that allows to query the state
If this "something" is a code that is managed by dependency, create a mock of this dependency and verify that it was called with the expected parameters.
Take a look at the Mockito Documentation (https://static.javadoc.io/org.mockito/mockito-core/3.0.0/org/mockito/Mockito.html#13)
When using a Spy you can 'replace' a method in the same class that is under test.
#ExtendWith(MockitoExtension.class)
public class Test {
class MyClass {
public void a() {
b();
}
public void b() {
}
}
#Test
public void test() {
MyClass testClass = new MyClass();
MyClass spy = Mockito.spy(testClass);
Mockito.doNothing().when(spy).b();
spy.a();
Mockito.verify(spy, Mockito.times(1)).b();
}
}
So whether that is something that should be done is a different question ;)
I think it highly depends on what method B() is actually doing and whether that is supposed be part of MyClass in the first place.
Either its not possible without mocking the whole CUT
In this case we do not mock the whole CUT only the method you do not want to be called.
Reason asking is that wherever i read about Mockito and similar tools, it says one should never mock CUT but its dependencies (that part is clear).
I believe this statement is not entirely accurate in correlation with spying.
The whole point of spying in my eyes is to use it on the class under test. Why would one want to spy on a dependecy that is not even supposed to be part of the test in the first place?
I've covered the internal implementation of my class with UnitTests. Is it still useful to test my public interface now (which is one function that is little more then a chain of calls to the internal methods)?
It feels like I would be adding additional tests that test the same thing(s).
Or is testing the public interface more an integration test (even though I've stubbed my data access so it's all processed in memory) in that way that it tests whether all the UnitTested methods work well together?
Example:
internal bool internalCheck() {
// complex logic that is being unit tested
}
internal void internalDoSomething() {
// do stuff. is being unit tested
}
public void DoIt() {
if (internalCheck()) {
internalDoSomething();
}
}
Now if I am going to add tests that test DoIt, I will basically end up retesting all logic flows for internalCheck and assert that when it returns true, the internalDoSomething is being called.
Hmm I think I've figured it out:
I need to mock the class itself and check just that the correct calls are being made, pretty much ignoring real inputs/outputs. To test the public method, rather than retesting the internalCheck, I use a mocking framework to have internalCheck return what flow I want to test and then verify that the correct methods have been called.
It depends how you have defined your unit. Usually the is the class, so this would still be a unit test.
Even if you have have tested the internal methods, it is still important to test the public interface, to make sure that the internal methods work together.
I have been wondering about the general use of stubs for unit tests vs using real (production) implementations, and specifically whether we don't run into a rather nasty problem when using stubs as illustrated here:
Suppose we have this (pseudo) code:
public class A {
public int getInt() {
if (..) {
return 2;
}
else {
throw new AException();
}
}
}
public class B {
public void doSomething() {
A a = new A();
try {
a.getInt();
}
catch(AException e) {
throw new BException(e);
}
}
}
public class UnitTestB {
#Test
public void throwsBExceptionWhenFailsToReadInt() {
// Stub A to throw AException() when getInt is called
// verify that we get a BException on doSomething()
}
}
Now suppose we at some point later when we have written hundreds of tests more, realize that A shouldn't really throw AException but instead AOtherException. We correct this:
public class A {
public int getInt() {
if (..) {
return 2;
}
else {
throw new AOtherException();
}
}
}
We have now changed the implementation of A to throw AOtherException and we then run all our tests. They pass. What's not so good is that the unit test for B passes but is wrong. If we put together A and B in production at this stage, B will propagate AOtherException because its implementation thinks A throws AException.
If we instead had used the real implementation of A for our throwsBExceptionWhenFailsToReadInt test, then it would have failed after the change of A because B wouldn't throw the BException anymore.
It's just a frightening thought that if we had thousand of tests structured like the above example, and we changed one tiny thing, then all the unit tests would still run even though the behavior of many of the units would be wrong! I may be missing something, and I'm hoping some of you clever folks could enlighten me as to what it is.
When you say
We have now changed the implementation of A to throw AOtherException and we then run all our tests. They pass.
I think that's incorrect. You obviously haven't implemented your unit test, but Class B will not catch AException and thus not throw BException because AException is now AOtherException. Maybe I'm missing something, but wouldn't your unit test fail in asserting that BException is thrown at that point? You will need to update your class code to appropriately handle the exception type of AOtherException.
If you change the interface of class A then your stub code will not build (I assume you use the same header file for production and stub versions) and you will know about it.
But in this case you are changing the behaviour of your class because the exception type is not really part of the interface. Whenever you change the behaviour of your class you really have to find all the stub versions and check if you need to change their behaviour as well.
The only solution I can think of for this particular example is to use a #define in the header file to define the exception type. This could get messy if you need to pass parameters to the exception's contructor.
Another technique I have used (again not applicable to this particular example) is to derive your production and stub classes from a virtual base class. This separates the interface from the implementation, but you still have to look at both implementations if you change the behaviour of the class.
It's normal that the test you wrote using stubs doesn't fail since it is intended to verify that object B communicates well with A and can handle the response from getInt() assuming that getInt() throws an AException. It is not intended to check if getInt() really throws an AException at any point.
You can call that kind of test you wrote a "collaboration test".
Now what you need to be complete is the counterpart test that checks if getInt() will ever throw an AException (or a AOtherException, for that matter) in the first place. It's a "contract test".
J B Rainsberger has a great presentation on the contract and collaboration tests technique.
With that technique here's how you'd typically go, solving the whole "false green test" problem :
Identify that getInt() now needs to throw a AOtherException rather than an AException
Write a contract test verifying that getInt() does throw a AOtherException under given circumstances
Write the corresponding production code to make the test pass
Realize you need collaboration tests for that contract test : for each collaborator using getInt(), can it handle the AOtherException we're going to throw ?
Implement those collaboration tests (let's say you don't notice there's already a collaboration test checking for AException at that point yet).
Write production code that matches the tests and realize that B already expects an AException when calling getInt() but not a AOtherException.
Refer to the existing collaboration test containing the stubbed A throwing an AException and realize it's obsolete and you need to delete it.
This is if you start using that technique just now, but assuming you adopted it from the start, there wouldn't be any real problem since what you'd naturally do is change the contract test of getInt() to make it expect AOtherException, and change the corresponding collaboration tests just after that (the golden rule is that a contract test always goes with a collaboration test so with time it becomes a no-brainer).
If we instead had used the real implementation of A for our
throwsBExceptionWhenFailsToReadInt test, then it would have failed
after the change of A because B wouldn't throw the BException anymore.
Sure, but this would have been a whole other kind of test -an integration test, actually. An integration test verifies both sides of the coin : does object B handle response R from object A correctly, and does object A ever respond that way in the first place ? It's only normal for a test like this to fail when the implementation of A used in the test starts to respond R' instead of R.
The specific example you have mentioned is a tricky one.. the compiler cannot catch it or notify you. In this case, you'd have to be diligent to find all usages and update the corresponding tests.
That said, this type of issue should be a fraction of the tests - you cannot wave away the benefits just for this corner case.
See also: TDD how to handle a change in a mocked object - there was a similar discussion on the testdrivendevelopment forums (linked in the above question). To quote Steve Freeman (of GOOS fame and a proponent of the interaction-based tests)
All of this is true. In practice, combined with a judicious
combination of higher level tests, I haven't seen this to be a big
problem. There's usually something bigger to deal with first.
Ancient thread, I know, but I thought I'd add that JUnit has a really handy feature for exception handling. Instead of doing try/catch in your test, tell JUnit that you expect a certain exception to be thrown by the class.
#Test(expected=AOtherException)
public void ensureCorrectExceptionForA {
A a = new A();
a.getInt();
}
Extending this to your class B you can omit some of the try/catch and let the framework detect the correct usage of exceptions.
I'm writing program arguments parser, just to get better in TDD, and I stuck with the following problem. Say I have my parser defined as follows:
class ArgumentsParser {
public ArgumentsParser(ArgumentsConfiguration configuration) {
this.configuration = configuration;
}
public void parse(String[] programArguments) {
// all the stuff for parsing
}
}
and I imagine to have ArgumentsConfiguration implementation like:
class ArgumentsConfiguration {
private Map<String, Class> map = new HashMap<String, Class>();
public void addArgument(String argName, Class valueClass) {
map.add(argName, valueClass);
}
// get configured arguments methods etc.
}
This is my current stage. For now in test I use:
#Test
public void shouldResultWithOneAvailableArgument() {
ArgumentsConfiguration config = prepareSampleConfiguration();
config.addArgument("mode", Integer.class);
ArgumentsParser parser = new ArgumentsParser(configuration);
parser.parse();
// ....
}
My question is if such way is correct? I mean, is it ok to use real ArgumentsConfiguration in tests? Or should I mock it out? Default (current) implementation is quite simple (just wrapped Map), but I imagine it can be more complicated like fetching configuration from kind of datasource. Then it'd be natural to mock such "expensive" behaviour. But what is preferred way here?
EDIT:
Maybe more clearly: should I mock ArgumentsConfiguration even without writing any implementation (just define its public methods), use mock for testing and deal with real implementation(s) later, or should I use the simplest one in tests, and let them cover this implementation indirectly. But if so, what about testing another Configuration implementation provided later?
Then it'd be natural to mock such "expensive" behaviour.
That's not the point. You're not mocking complex classes.
You're mocking to isolate classes completely.
Complete isolation assures that the tests demonstrate that classes follow their interface and don't have hidden implementation quirks.
Also, complete isolation makes debugging a failed test much, much easier. It's either the test, the class under test or the mocked objects. Ideally, the test and mocks are so simple they don't need any debugging, leaving just the class under test.
The correct answer is that you should mock anything that you're not trying to test directly (e.g.: any dependencies that the object under test has that do not pertain directly to the specific test case).
In this case, because your ArgumentsConfiguration is so simple, I'd recommend using the real implementation until your requirements demand something more complicated. There doesn't seem to be any logic in your ArgumentsConfiguration class, so it's safe to use the real object. If the time comes where the configuration is more complicated, then an approach you should probably take would be not to create a configuration that talks to some data source, but instead generate the ArgumentsConfiguration object from that datasource. Then you could have a test that makes sure it generates the configuration properly from the datasource and you don't need unnecessary abstractions.
This is a simplified version of a class I'm writing a unit test for
class SomeClass {
void methodA() {
methodB();
methodC();
methodD();
}
void methodB() {
//does something
}
void methodC() {
//does something
}
void methodD() {
//does something
}
}
While writing the unit tests for this class, I've mocked out objects using EasyMock used in each method. It was easy to set up the mock objects and their expectation
In method B,C,and D. But to test method A, I have to set up A LOT more mock objects and their expectations. Also, I’m testing method A in different conditions, meaning I have to setup the mock objects many times with different expectations.
In the end, my unit test becomes hard to maintain and pretty cluttered. I was wondering if anyone has or seen a good solution to this problem.
If I understand your question correctly, I think that this is a matter of design. The nice thing about unit testing is that writing tests often forces you to make your design better. If you need to mock too many things while testing a method it often means you should split your class into two smaller classes, which will be easier to test (and write, and maintain, and bugfix, and reuse, etc.).
In your case, the method A seems to be at a higher level than methods A, B, C. You can consider removing it to a higher level class, that would wrap SomeClass:
class HigherLevelClass {
ISomeClass someClass;
public HigherLevelClass(ISomeClass someClass)
{
this.someClass = someClass;
}
void methodA() {
someClass.methodB();
someClass.methodC();
someClass.methodD();
}
}
class SomeClass : ISomeClass {
void methodB() {
//does something
}
void methodC() {
//does something
}
void methodD() {
//does something
}
}
Now when you are testing methodA all you need to mock is the small ISomeClass interface and the three method calls.
You could extract common setup code into separate (possibly parametrized) methods, then call them whenever appropriate. If the tests for methodA have a very different fixture from the tests of the other methods, there may not be much to put into the #Before method itself, so you need to call the appropriate combination of setup helper methods from the test methods themselves. It is still a bit cumbersome, but better than duplicating code all over the place.
Depending on what unit test framework you use, there may be other options too, but the above should work with any framework.
This is an example of a Fragile test because the mock setups have too intimate knowledge of the SUT.
I don't know EasyMock, but with Moq you don't need to setup void methods. However, with Moq the methods would have to be public or protected and virtual.
For each test you're writing, consider the behaviour which is valuable for that test. You'll have some contexts you're setting up which the behaviour relies on, and some outcomes as a result of the behaviour that you want to verify.
Set up relevant contexts, verify the outcomes, and use NiceMocks for everything else.
I prefer Mockito (Java) or Moq (.NET) which work this way by default. Here's Mockito's page on Mockito vs. EasyMock so you can get the idea (EasyMock didn't have NiceMock before Mockito came along):
http://code.google.com/p/mockito/wiki/MockitoVSEasyMock
You can probably use EasyMock's NiceMock in a similar way. Hopefully this will help you detangle your tests. You can always import both frameworks and use them alongside each other / incrementally switch over if it helps.
Good luck!
I’m testing method A in different conditions, meaning I have to setup the mock objects many times with different expectations.
If you care of what methodA is doing and which collaborator function has to be called then you have to setup different expectations... I don't see how you can skip this step?!
If you testLogout you would expect a call to myCollaborator.logout() otherwise if you testLogin you would expect something like myCollaborator.login().
If you have many methods with lots/different expectations maybe is the case to split your class in collaborators