Embedded C/C++ Unit Testing Basics

In software engineering, unit testing is a software testing method by which individual units of source code, sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures, are tested to determine whether they are fit for use. 

Framework-Less Unit Tests

A unit test is a test that covers a single component or small piece of functionality in an application. In a framework-less unit test, there is no predefined structure or set of rules to follow. This means that the test can be written in any language and does not require a specific testing framework. 

• Framework-less unit tests are often used to test specific functionality in a system that is not easily testable using a traditional testing framework. 
• For example, if you want to test how a system responds to a specific input, you can write a unit test that sends that input to the system and then checks the output. 
• Framework-less unit tests can be useful when you want to test something that is not easily testable using a traditional testing framework. However, they can also be more difficult to write and maintain than traditional unit tests.

There are a number of reasons why developers might choose to write unit tests without the use of a framework. 

• In some cases, the code under test may be too simple to warrant the overhead of a framework.
• In other cases, the developer may be more interested in testing the code itself, rather than the framework surrounding it.
• One advantage of writing unit tests without a framework is that it can help to keep the tests themselves simple and focused. 
• Without the need to worry about setting up and configuring a testing framework, developers can spend more time thinking about the individual test cases and what they are trying to achieve. This can lead to more robust and reliable tests. 
• Another advantage is that, without the use of a framework, it can be easier to debug tests. This is because the developer has full control over the code and can step through it line by line to find any issues. 
• This can be a particularly useful approach when working with legacy code that may be difficult to test using a framework.
• Finally, writing unit tests without a framework can also be quicker and easier than using a framework. This is because there is no need to spend time configuring and setting up the framework. This can be a significant advantage when working on a tight deadline. 

While there are a number of advantages to writing unit tests without a framework, there are also some disadvantages. 

• One of the main disadvantages is that, without a framework, it can be more difficult to reuse tests. This is because the developer would need to copy and paste the code for each test, rather than being able to reuse a testing framework.
• Another disadvantage is that, without a framework, it can be more difficult to maintain the tests. This is because each test would need to be updated individually, rather than being able to update the tests all at once using a testing framework.

Overall, there are both advantages and disadvantages to writing unit tests without a framework. Ultimately, the decision of whether or not to use a framework should be based on the individual needs of the project.

Minimal Unit Test  

A minimal unit test is a test that exercises the smallest possible unit of code in your application. This usually means testing a single function, but it could also mean testing a small group of closely related functions. 

• The purpose of a minimal unit test is to ensure that the unit of code under the test behaves as expected. 
• This usually means verifying that the function returns the correct output when given a specific input. 
• A minimal unit test should be self-contained, meaning that it should not rely on any external state or data. This ensures that the test is repeatable and can be run in any environment. 
• A minimal unit test should also be easy to understand and maintain. This means keeping the test focused on a single behavior, and avoiding duplication or complexity. 
• Finally, a minimal unit test should be runnable automatically and should not require any manual intervention. This ensures that the test can be run frequently and will not slow down the development process.

Example of a Minimal Unit Test:

public class MyClassTest {
   @Test
   public void testMyClass() {
       MyClass myClass = new MyClass();
       assertEquals(expected, myClass.myMethod());
   }
}

In this example, we are testing the myMethod() method of the MyClass class. An instance of MyClass is created and then call myMethod(). The assertEquals() method is used to verify that the expected result is equal to the actual result. Minimal Unit Tests are a valuable tool for testing and debugging code. By keeping them small and specific, they can help to ensure that code is functioning correctly and identify exactly where problems are occurring.

Unit Testing Best Practices 

There are many different ways to write unit tests, but there are some common best practices that can help make your unit tests more effective.

1. Write tests that are small and focused: Each test should only test one thing, and it should be as small as possible. This makes it easier to understand what the test is doing, and it makes it more likely that the test will catch errors.
2. Write tests that are independent: Each test should be independent of the others. This means that you should not have to run one test before another and that you should not have to set up data for other tests.
3. Write tests that are repeatable: You should be able to run a test multiple times and get the same results each time. This means that your tests should not rely on external data that could change, such as the current date or time.
4. Write tests that are self-checking: Your tests should check their own results to make sure that they are correct. This means that you do not have to manually check the results of each test.
5. Write tests that are readable: Your tests should be easy to understand, both for yourself and for others who may need to read them. This means using clear and descriptive names for your tests and variables. By following these best practices, you can write unit tests that are more effective and easier to maintain. 

Stubs, Fakes, and Mocks

Stubs, fakes, and mocks are all ways of creating test doubles. Test doubles are dummy objects that stand in for real objects in order to test a particular piece of code.

• Stubs: Stubs provide canned responses to calls made during the test and are typically used to help test code that makes external calls. For example, if your code makes a call to an external API, you can stub out that call and have it return a predefined response. This way, you don’t have to actually make the call to the API, and you can test your code without depending on the external service.
• Fakes: Fakes are similar to stubs, but they provide more realistic responses. For example, a fake database might return data that looks like real data, even though it’s not actually stored in a real database. This can be useful for testing code that interacts with a database, without having to set up a real database.
• Mocks: Mocks are the most sophisticated type of test double. They not only provide canned responses, but they also track how they are called and can verify that they are called correctly. This is useful for testing code that has complex interactions with other code. For example, you can use a mock to verify that a particular method is called with the correct arguments, in the correct order.

What is Embedded C/C++ Unit Testing?

Embedded C/C++ unit testing is a process of validating the functionality of individual units of code by creating test cases. These test cases exercise the functionality of the code and check for expected results. The purpose of embedded C/C++ unit testing is to find and fix defects early in the development cycle, before they can cause problems in the final product. There are many different approaches to embedded C/C++ unit testing, but all share some basic features. First, a test driver is written to provide a controlled environment for running the tests. This driver calls the functions under test and checks the results against expected values. Second, a test suite is created containing all of the tests that need to be run. This suite is then executed by the test driver.

• One common approach to embedded C/C++ unit testing is called “stubs and drivers.” In this approach, stubs are used to replace any external dependencies of the code under test. This allows the code to be tested in isolation from other parts of the system. Drivers are used to providing inputs to the code under test and to check its outputs.
• Another common approach is called “mocks and fakes.” In this approach, mocks are used to simulate external dependencies of the code under test. This allows the code to be tested in isolation from other parts of the system. Fakes are used to provide inputs to the code under test and to check its outputs.

How to Get Started with Embedded C/C++ Unit Testing?

If you’re new to unit testing, the process of getting started can seem daunting. But with a few tips and tricks, you can be up and running in no time. Here are a few things to keep in mind when getting started with embedded C/C++ unit testing:

• Choose the right unit testing framework for your project. There are many different frameworks available, so it’s important to select one that will work well for your specific project.
• Write testable code. This may seem like a no-brainer, but it’s important to keep this in mind when writing code for your project. Make sure your code is modular and easy to test.
• Set up a continuous integration (CI) server. This will help automate the process of running tests and building your project.
• Write lots of tests. The more tests you have, the more coverage you’ll have for your codebase. Try to think of all the different scenarios that could occur and write tests accordingly.

Real-World Unit Test Example

A real-world unit test example would be testing a function that calculates the average of a set of numbers. The unit test would check that the function returns the expected result when given different sets of numbers. A real-world unit test might involve testing a method that calculates the monthly payment on a loan. The test would provide various loan amounts, interest rates, and loan terms, and compare the results of the method to the expected results. Let’s say you are a developer and you are developing an e-commerce website. There are many things that need to be built, but one of the first things you need to build is a calculation engine that calculates the total cost of a user’s order, including shipping and taxes.

• You could write a unit test for this calculation engine that verifies that it correctly calculates the total cost of an order, including shipping and taxes.
• Or, let’s say you are a developer and you are developing a login system for a website. You could write a unit test for this login system that verifies that it correctly logs a user in and out of the website.
• Or, let’s say you are a developer and you are developing a user registration system for a website. You could write a unit test for this registration system that verifies that it correctly registers a user on the website.

Setting Up CppUTest

CppUTest is a C/C++-based unit testing framework for software projects. It is designed to provide a great deal of flexibility and power in a relatively small package. CppUTest is released under the Apache License, version 2.0. The basic idea behind CppUTest is to write tests in C++ code using a set of simple macros. These macros generate code that interacts with your production code to exercise different paths and verify expected results. Your test code is then linked with a CppUTest library to produce an executable test program. You can then run this test program to exercise the tests you’ve written and see the results. CppUTest can generate output in multiple formats, including JUnit XML for use with continuous integration servers. CppUTest also supports mocking of C/C++ code using the Google Mock framework. This allows you to write tests for code that has dependencies on other modules, without needing to link to or include the production code for those modules. 

Common Issues with C/C++ Unit Tests

• Difficulty in mocking dependencies: In C/C++, it can be difficult to mock out dependencies when writing unit tests. This can lead to tests that are not as isolated as they should be, and can make it difficult to test edge cases.
• Lack of a standard unit testing framework: There is no standard unit testing framework for C/C++. This can make it difficult to find and use the right tools for your project.
• Lack of support for test-driven development: C/C++ does not have great support for test-driven development. This can make it difficult to write tests that are comprehensive and that cover all the corner cases.
• Memory leaks: If the code being tested is not properly freeing memory, this can lead to memory leaks.
• Resource leaks: If the code being tested is not properly releasing resources, this can lead to resource leaks.
• Deadlocks: If the code being tested is not properly handling concurrency, this can lead to deadlocks.

Benefits of Embedded C/C++ Unit Testing

• Early bug detection: Embedded C/C++ unit testing can help you catch bugs early and prevent them from becoming expensive problems later on. 
• Ensure code performs as intended: By writing and running tests for your embedded C/C++ code, you can ensure that your code is doing what it’s supposed to do and that it’s robust enough to handle real-world conditions. 
• Improve the quality of code: Embedded C/C++ unit testing can help you improve the quality of your code by making it easier to find and fix coding errors. 
• Increase confidence in code: By using a well-designed unit test suite, you can also increase your confidence in the code, which can lead to fewer unexpected problems when the code is released into the wild.