Mocking BiFunction with Spock Java/Groovy

user_961380 0
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Pretty new to Spock. Trying to mock a function that returns a BiFunction unsuccessfully.
The function looks like

public interface myInterface { 
  Optional<BiFunction<Object, Object, Object>> myAwesomeFunc()
}

Trying to mock like 

def mockBiFunction = Mock(BiFunction)
mockMyInterface.myAwesomeFunc >> mockBiFunction 
mockBiFunction.apply(*_) >> mockReturnVal

This results in

No signature of method: com.sun.proxy.$Proxy49.apply() is applicable for argument types: (org.spockframework.lang.SpreadWildcard) values: [*_]
Possible solutions: apply(java.lang.Object, java.lang.Object), any(), any(groovy.lang.Closure), every(), tap(groovy.lang.Closure), every(groovy.lang.Closure)
groovy.lang.MissingMethodException: No signature of method: com.sun.proxy.$Proxy49.apply() is applicable for argument types: (org.spockframework.lang.SpreadWildcard) values: [*_]
Possible solutions: apply(java.lang.Object, java.lang.Object), any(), any(groovy.lang.Closure), every(), tap(groovy.lang.Closure), every(groovy.lang.Closure)

Tried with

mockBiFunction(*_) >> mockReturnVal

That doesn't work either.

Edit: Tried with

mockBiFunction.apply(object1, object2) >> mockReturnVal

This fails with

Cannot invoke method rightShift() on null object
java.lang.NullPointerException: Cannot invoke method rightShift() on null object

When I have mocked it then why is it null ??

spock java-11 testing groovy mocking
2 Answers

Actually, your interface method returns an Optional, not a BiFunction. More precisely, it returns Optional<BiFunction<Object, Object, Object>>. Therefore, your interface mock needs to return an Optional as well when stubbing myAwesomeFunc(). That is what IMO is wrong with your code.

Your own answer does not look logical to me, but that might be because both in your question and your answer you only provided incoherent sets of snippets instead of a proper MCVE. Please do learn how to ask good questions. You seem to be an experienced developer, wrestling with optionals of bi-functions etc. Therefore, you ought to know how to make your problem reproducible. If you are unable to do that, you cannot expect good answers or people even feeling inclined to try.

Anyway, here is my take:

package de.scrum_master.stackoverflow.q71602791

import spock.lang.Specification

import java.util.function.BiFunction

class BiFunctionMockTest extends Specification {
  def "mock BiFunction"() {
    given:
    def biFunction = Mock(BiFunction) {
      apply(*_) >> "dummy"
    }
    def myInterface = Mock(MyInterface) {
      myAwesomeFunc() >> Optional.of(biFunction)
    }
    def underTest = new MyInterfaceUser(myInterface: myInterface)

    expect:
    underTest.doSomething().get().apply("foo", "bar") == "dummy"
  }

  interface MyInterface {
    Optional<BiFunction<Object, Object, Object>> myAwesomeFunc()
  }

  static class MyInterfaceUser {
    MyInterface myInterface

    def doSomething() {
      myInterface.myAwesomeFunc()
    }
  }
}
user_10826810

Ah looks like all I had to do was to use a function as the mock return value from the BiFunction so something like following works

def mockMyAwesomeFunc = abc -> mockReturnVal 
mockBiFunction.apply(object1, object2) >> mockMyAwesomeFunc

instead of doing

mockBiFunction.apply(object1, object2) >> mockReturnVal

Feeling really stupid now !!

Edit -- Updating the answer to more closely reflect the actual working code - this is what worked

def mockBiFunction = Mock(BiFunction)
mockMyInterface.myAwesomeFunc >> Optional.of(mergeBiFunction)
mergeBiFunction.apply(_, _) >> (a, b) -> {
    return mockValue
}
user_9613800
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