CppUMock

CppUMock is a lightweight C/C++ unit testing mock framework that is mainly used for creating mock functions and verifying interactions in unit tests. It is commonly used in combination with unit testing frameworks like CppUTest.

CppUMock (often written as CppUMock) is designed for C and C++ codebases that enables developers to:

• Replace real functions with mock versions
• Set expectations on function calls
• Control return values and behaviors
• Verify how code interacts with dependencies

It is especially useful in embedded systems and legacy C/C++ projects.

Why we use CppUMock?

CppUMock is used because:

• It allows unit testing of legacy or C code
• Helps isolate dependencies (hardware, OS calls, APIs)
• Supports test-driven development (TDD)
• Works well in resource-constrained environments (like embedded systems)

It is particularly valuable when:

• You cannot easily use modern C++ mocking frameworks
• You are testing low-level system code

When should we use CppUMock?

Use CppUMock when:

1. You are working with C or C-style C++

• Legacy systems
• Embedded firmware

2. You need lightweight mocking

• Minimal overhead is important

3. You are using CppUTest

• It integrates tightly with CppUTest framework

4. You need to mock external dependencies

• Hardware drivers
• System calls
• Network interfaces

Avoid or reconsider if:

• You are working on modern C++ projects
• You prefer richer frameworks like Trompeloeil or Google Mock

Key Features of CppUMock

1. Function-level mocking

Allows replacing C/C++ functions with mock implementations

2. Expectation setting

You can define:

• How many times a function is called
• What parameters are expected

3. Return value control

Mock functions can return predefined values

4. Integration with CppUTest

Designed to work seamlessly with: CppUTest

5. Lightweight design

Very small footprint compared to modern C++ frameworks

Key Components of CppUMock

1. Mock functions

Used to replace real functions:

int myFunction(int a);

2. Expectations

Define expected calls:

Function must be called
Arguments must match

3. Stubs

Provide default behavior when no specific expectation is set

4. Return values

Control what mocked functions return

CppUMock Example

#include "CppUTest/TestHarness.h"
#include "CppUTestExt/MockSupport.h"

int hardwareRead(int id);

TEST_GROUP(MyGroup)
{
    void teardown()
    {
        mock().clear();
    }
};

TEST(MyGroup, ReadSensorTest)
{
    mock().expectOneCall("hardwareRead")
         .withParameter("id", 1)
         .andReturnValue(100);

    int result = hardwareRead(1);

    LONGS_EQUAL(100, result);

    mock().checkExpectations();
}

Advantages of CppUMock

1. Lightweight: Very small and efficient

2. Ideal for embedded systems: Works well in constrained environments

3. Good C compatibility: Supports both C and C++ code

4. Tight integration with CppUTest: Simplifies test setup

5. Simple mocking model: Easy for function-level mocking

Disadvantages of CppUMock

1. Limited modern C++ support: Not designed for advanced C++ features

2. Less expressive than modern frameworks: Compared to Trompeloeil or Google Mock

3. Function-based only: No advanced object-oriented mocking features

4. Smaller community: Less active development compared to modern tools

Alternatives to CppUMock

1. Trompeloeil

• Modern C++ mocking
• Strong type safety
• Better for C++ projects

2. Google Mock (gMock)

• Most widely used C++ mocking framework
• Feature-rich and powerful

3. FakeIt

• Simple syntax
• Lightweight modern C++ mock library

4. FFF (Fake Function Framework)

• Very lightweight function mocking (C-focused)