Feature: Add a way to mock a constructor with defined values

[Tryle]

Prerequisites

Please answer the following questions for yourself before submitting an issue.

• I am running the latest version
• I checked the documentation and found no answer
• I checked to make sure that this issue has not already been filed

Expected Behavior

Actually we can mock constructors but there is no way to handle constructors parameters. Something like:

class MockCls(val minValue: Int) {
  fun add(a: Int, b: Int) = minValue + a + b
}

mockkConstructor(MockCls::class)

every { anyConstructed<MockCls>(10).add(1, 2) } returns 14

assertEquals(14, MockCls(10).add(1, 2)) // note new object is created

verify { anyConstructed<MockCls>(10).add(1, 2) } // success
verify { anyConstructed<MockCls>(5).add(1, 2) } // fail

For reference there is a question on SO about that.

[mpost]

I am facing the same requirement to retrieve the constructor arguments for the created class. It is good to see a feature request which is not closed immediately so it seems to be at least feasible. Hope to see it soon.

[pascalpfeil]

I need this, too.

[erikhuizinga]

I'm not sure, but if I read the readme correctly, the current implementation of mockkConstructor can only create one mock for all constructed instances, am I right? By that one mock, I mean the object you get through the anyConstructed function.

This, of course, is not ideal for true power to the user. Ideally we could do something like this:

// Note this class has two constructors
class Cls() {
    constructor(a: Any?) : this()
}

@Test 
fun `some test`() = mockkConstructors(Cls::class) {
    val mock1 = mockk<Cls>()
    val mock2 = mockk<Cls>()
    val a = 0

    every { Cls() } returns mock1
    every { Cls(a) } returns mock2
}

Notes:

• Note the 's' in mockkConstructors: this would mock all available constructors, which can potentially be many.
  • OTOH, as a MockK user I'd want the ability to specifically mock a constructor with a specific signature.
• Note that I return different instances in different cases (in this case mockks, but of course, these can be any valid instance).

[oleksiyp]

Yes, you are right. The underlying mocking stub is only one. And all the calls from created objects via mockkConstructor are delegated to this stub.

Returning arbitrary object/mocks as a result of the constructor calls is not possible. But attaching different stubs is possible.

I've made an attempt to implement a variety of constructors in a simple way: #267
But seems full rewrit\e is needed. This implementation lacks a few things.

I have an idea that constructor call should be somehow indistinguishable from method call at the level of DSL engine. This will unify it the way you can apply all the machinery with matchers.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. If you are sure that this issue is important and should not be marked as stale just put an important tag.

[erikhuizinga]

@Stale[bot] come on man bot! No activity means no activity, but not that an issue should be closed! This way active issues or even bugs might lose visibility.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. If you are sure that this issue is important and should not be marked as stale just ask to put an important label.

[darrengyl]

We need this! It will be really useful to test constructors with parameters

[bboyairwreck]

can i asked why this was closed? This would be really nice functionality that has a real use cases. Stop closing this ticket bot

[oleksiyp]

Check #356

[espertus]

I would like this too.

[Richrocksmy]

In relation to this, when mocking constructors that are not the default constructor ie they have parameters the mocking doesn't appear to work and instead the real code gets called.

I think that adding the ability to mock constructors individually would fix this issue.

[marklapasa]

bump - would like to see this too

[rkokhatskyi]

+1 for this feature

[thesultanster]

+1 for this as well

[davidcre]

+1 the current implementation of constructor mocking is not enough.
Thank you for considering this feature 👍

[noah-iam]

I am facing the same issue while mocking the class with parameter constructor.

io.mockk.MockKException: No matching constructors found:

[miva2]

I tried to write this but apparently it's not possible
every { SomeClass(param1, param2) } returns SomeClassMock

I haven't used MockK a lot yet but expected it to work like that.

[trietbui85]

+1 for this feature.

[distante]

I am also very interested in this.

[othiagosouto]

+1

[JureSencar]

+1

The workaround I use (in case I own the code) is to define a factory method with @VisibleForTesting to the companion object of the class and mockk that. Of course, changing source for the sake of testing is not nice and it is not an option if you don't own the code. Thus, I am definitively interested in this feature.

[kenaiX]

+1

[martinezdputraa]

+1

[JanCizmar]

+1

[om32]

+1

[Jethril]

+1

[campino-rocks]

+1

[chmod]

+1

[Diones]

+1

[gregorgrisza]

+1

[konstantin-tkachuk]

+1

[felipezad]

+1

[FGuyet]

+1!

[olgachrostowska-meelogic]

+1!

[AshokKumarMandava]

+1

[KevinBassaDevelopment]

+1

[Bebooo43]

+1

[erikhuizinga]

Has this partially/entirely been fixed in v1.11.0?

[Raibaz]

Yep, v1.11.0, just released, adds constructedWith that fixes this.