Check the input parameters with groovy.mock.interceptor - unit-testing

Question

I'm trying to have some unit tests using groovy.mock.interceptor. I want to assert that a function was indeed called with some specific values as arguments. I can't find how to do that. Any help?
This is what it looks like:
import groovy.mock.interceptor.MockFor
import org.junit.Test
class MyClassTest extends GroovyTestCase {
#Test
void test_correctness_of_passed_arguments() {
def mock = new MockFor(MyClass)
mock.ignore('main')
mock.demand.myFunction{a, b, c -> '0'} // Is this where I should enforce the input params?
mock.use {
def foo = new MyClass()
foo.main() // <--- this is in there that it gets executed
}
mock.expect.verify()
mock.demand.recorded[0] // <--- can I get what has been passed afterwards?
}
}

Answer 1

You can't achieve expected behavior with MockFor class. Ignoring main method has one significant effect - inner method myFunction gets executed, but it happens without a presence of MockInterceptor. You can put a breakpoint in groovy.mock.MockProxyMetaClass class in the beginning of invokeMethod (line 74) and run a debugger to see what happens.
public Object invokeMethod(final Object object, final String methodName, final Object[] arguments) {
if (null == interceptor && !fallingThrough) {
throw new RuntimeException("cannot invoke method '" + methodName + "' without interceptor");
}
Object result = FALL_THROUGH_MARKER;
if (interceptor != null) {
result = interceptor.beforeInvoke(object, methodName, arguments);
}
if (result == FALL_THROUGH_MARKER) {
Interceptor saved = interceptor;
interceptor = null;
boolean savedFallingThrough = fallingThrough;
fallingThrough = true;
result = adaptee.invokeMethod(object, methodName, arguments);
fallingThrough = savedFallingThrough;
interceptor = saved;
}
return result;
}
Invoking foo.main() method in the mock.use {} block invokes this method for non-null interceptor. The result returned by interceptor.beforeInvoke() is equal to FALL_THROUGH_MARKER because main method is marked as ignored. In this case interceptor is set to null temporarily and the method gets invoked in a regular way - it invokes inner myFunction method, but this fact is not recorded due to null interceptor at this point.
Basically, you treat mock object in your test case not as a mock, but rather as a spy object. Groovy standard mocking library does not support spy objects, but you can use e.g. Spock Framework to write tests using spy objects. The test you have shown in the question could look like this using Spock:
import spock.lang.Specification
class ExampleSpec extends Specification {
static class MyClass {
def main() {
return myFunction(0, 0 ,0)
}
def myFunction(def a, def b, def c) {
return '2'
}
}
def "should call myFunction with specific parameters"() {
given:
def foo = Spy(MyClass)
when:
foo.main()
then:
1 * foo.myFunction(0, 0, 0)
and:
0 * foo.myFunction(1,0,0)
}
}
It executes a real foo.main() method, but it mocks foo.myFunction() method and records invocations and tests if the method got invoked with correct parameters - it records that it got invoked once with parameters (0, 0, 0) and that it was not invoked with parameters (1, 0, 0).
IMPORTANT: If you create mock/spy objects from classes and not interfaces, then you need to add cglib-nodep dependency together with Spock.

Answer 2

Okay, this is doable as mock.demand.myFunction takes a normal Closure.
I ended up with something like this:
import groovy.mock.interceptor.MockFor
import org.junit.Test
class MyClassTest extends GroovyTestCase {
#Test
void test_correctness_of_passed_arguments() {
def mock = new MockFor(MyClass)
mock.ignore('main')
def res = []
// the mocked function stores its values in `res` and returns '0'
mock.demand.myFunction(4) {a, b, c ->
res.add([a, b, c])
'0'
}
mock.use {
def foo = new MyClass()
foo.main() // <--- this is in there that it gets executed
}
mock.expect.verify()
res[0] // <--- I can then access the values there
}
}
In the above example, I request myFunction to be called 4 times.