GoogleTest EXPECT_CALL throws uninteresting call warning and returns 0 calls

Question

I am trying to Mock an external library and test what APIs of the library are being called from my interfaces and I have come across a behavior (first time using mocking) that I can't seem to understand. So, I have a mock class like this:

class VulkanLibMock {
public:
    MOCK_METHOD(VkResult, vkCreateDescriptorSetLayout, (VkDevice, const VkDescriptorSetLayoutCreateInfo *, const VkAllocationCallbacks *, VkDescriptorSetLayout *pSetLayout));
    
    MOCK_METHOD(VkResult, vkCreateDescriptorPool, (VkDevice, const VkDescriptorPoolCreateInfo *, const VkAllocationCallbacks *, VkDescriptorPool *));
};

and a test base class to handle values:

class VulkanBaseTest : public ::testing::Test {
public:
    VulkanBaseTest() {
        vulkanLibMock = new ::testing::NiceMock<VulkanLibMock>;
    }
    
    ~VulkanBaseTest() {
        delete vulkanLibMock;
        vulkanLibMock = nullptr;
    }
    
public:
    static VulkanLibMock *vulkanLibMock;
};

So, I inherited a test class from it:

class VulkanDescriptorManagerTests : public VulkanBaseTest {
public:
    VulkanDescriptorManagerTests() = default;
};

and added one test case:

TEST_F(VulkanDescriptorManagerTests, MyTest) {

ON_CALL(*vulkanLibMock, vkCreateDescriptorSetLayout).WillByDefault([](VkDevice, const VkDescriptorSetLayoutCreateInfo *, const VkAllocationCallbacks *, VkDescriptorSetLayout *) {
  std::cout << "Called: vkCreateDescriptorSetLayout";
  return VK_SUCCESS;
});
    
ON_CALL(*vulkanLibMock, vkCreateDescriptorPool).WillByDefault([](VkDevice, const VkDescriptorPoolCreateInfo *, const VkAllocationCallbacks *, VkDescriptorPool *) {
  std::cout << "Called: vkCreateDescriptorPool";
  return VK_SUCCESS;
});
    
// this is the class that I am trying to test
VulkanDescriptorManager manager(nullptr);    
EXPECT_CALL(*vulkanLibMock, vkCreateDescriptorSetLayout);

}

If I don't use NiceMock, I get the following warning when running tests

Called: vkCreateDescriptorSetLayout <-- cout in `ON_CALL`
Uninteresting mock function call - taking default action specified at:
VulkanDescriptorManager.test.cpp:12:
    Function call: vkCreateDescriptorSetLayout(NULL, 0x7ffeefbfec50, NULL, 0x7ffeefbfedf0)
          Returns: 0
NOTE: You can safely ignore the above warning unless this call should not happen.  Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call.  See https://github.com/google/googletest/blob/master/docs/gmock_cook_book.md#knowing-when-to-expect for details.
Called: vkCreateDescriptorSetLayout <-- cout in `ON_CALL`
GMOCK WARNING:
Uninteresting mock function call - taking default action specified at:
VulkanDescriptorManager.test.cpp:12:
    Function call: vkCreateDescriptorSetLayout(NULL, 0x7ffeefbfec20, NULL, 0x7ffeefbfedf8)
          Returns: 0
NOTE: You can safely ignore the above warning unless this call should not happen.  Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call.  See https://github.com/google/googletest/blob/master/docs/gmock_cook_book.md#knowing-when-to-expect for details.
Called: vkCreateDescriptorPool <-- cout in `ON_CALL`
GMOCK WARNING:
Uninteresting mock function call - taking default action specified at:
VulkanDescriptorManager.test.cpp:17:
    Function call: vkCreateDescriptorPool(NULL, 0x7ffeefbfeca0, NULL, 0x7ffeefbfee00)
          Returns: 0
NOTE: You can safely ignore the above warning unless this call should not happen.  Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call.  See https://github.com/google/googletest/blob/master/docs/gmock_cook_book.md#knowing-when-to-expect for details.

And, I get an error regardless of using NiceMock:

Actual function call count doesn't match EXPECT_CALL(*vulkanLibMock, vkCreateDescriptorSetLayout)...
         Expected: to be called once
           Actual: never called - unsatisfied and active

What am I missing here? I know that the function is called since can see the output of cout statement in ON_CALL implementation. Why does EXPECT_CALL thinks that the function is not called?

EDIT: VulkanDescriptorManager (simplified):

VulkanDescriptorManager(VkDevice device) {
  // global library functions
  VkDescriptorSetLayoutCreateInfo sceneCreateInfo{};
  vkCreateDescriptorSetLayout(device, &createInfo, nullptr, &this->sceneDescriptorSet);

  VkDescriptorSetLayoutCreateInfo materailCreateInfo{};
  vkCreateDescriptorSetLayout(device, &materailCreateInfo, nullptr, &this->materialDescriptorSet);

  // same logic for vkCreateDescriptorPool
}

The called functions are global and were coming from library. In order to be able to test them, I unlinked the library and created my own implementation for the functions:

// this is in my global library mock file:

VkResult vkCreateDescriptorSetLayout(
    VkDevice device, const VkDescriptorSetLayoutCreateInfo *pCreateInfo,
    const VkAllocationCallbacks *pAllocator,
                                     VkDescriptorSetLayout *pSetLayout) {
    // Calls the function in mock that is accessible from
    // VulkanBaseTest's static variable
    return VulkanBaseTest::vulkanLibMock->vkCreateDescriptorSetLayout(device, pCreateInfo, pAllocator, pSetLayout);
}


VkResult vkCreateDescriptorPool(VkDevice device,
                                  const VkDescriptorPoolCreateInfo *pCreateInfo,
                                  const VkAllocationCallbacks *pAllocator,
                       VkDescriptorPool *pDescriptorPool) {
    return VulkanTestFixture::vulkanLibMock->vkCreateDescriptorPool(device, pCreateInfo, pAllocator, pDescriptorPool);
}

Answer 1

According to the gmock doc

Important note: gMock requires expectations to be set before the mock functions are called, otherwise the behavior is undefined. Do not alternate between calls to EXPECT_CALL() and calls to the mock functions, and do not set any expectations on a mock after passing the mock to an API.

Your code need to adjust these two lines sequence from:

VulkanDescriptorManager manager(nullptr);    
EXPECT_CALL(*vulkanLibMock, vkCreateDescriptorSetLayout);

to:

EXPECT_CALL(*vulkanLibMock, vkCreateDescriptorSetLayout);
VulkanDescriptorManager manager(nullptr);    

The doc has also explained why they use such design:

Why does gMock work like that? Well, specifying the expectation beforehand allows gMock to report a violation as soon as it rises, when the context (stack trace, etc) is still available. This makes debugging much easier.