throwtheswitch libraries: Unity, Cmock, Ceedling, etc http://www.throwtheswitch.org/
UNITY, Unit Testing for C (especially Embedded Software) http://www.throwtheswitch.org/unity/
CMock, Automated Mock & Stub Generation For C http://www.throwtheswitch.org/cmock/
Ceedling, build system for C projects http://www.throwtheswitch.org/ceedling
Books for learning Unit Testing (in particular Test-Driven Development) for Embedded Development in C. http://www.throwtheswitch.org/books
Test-Driven Development for Embedded C, James W. Grenning https://pragprog.com/book/jgade/test-driven-development-for-embedded-c
Embedded Testing with Unity and CMock, Mark VanderVoord http://www.lulu.com/shop/mark-vandervoord/embedded-testing-with-unity-and-cmock/paperback/product-14408590.html
Unit-testing (embedded) C applications with Ceedling https://dmitryfrank.com/articles/unit_testing_embedded_c_applications
Modern unit testing in C with TDD and Ceedling http://www.embedded.com/design/programming-languages-and-tools/4442825/2/Modern-unit-testing-in-C-with-TDD-and-Ceedling
Mocking Embedded Hardware Interfaces with Ceedling and CMock http://www.electronvector.com/blog/mocking-embedded-hardware-interfaces-with-ceedling-and-cmock
Try Embedded Test-Driven Development Right Now with Ceedling http://www.electronvector.com/blog/try-embedded-test-driven-development-right-now-with-ceedling
The mock object approach to test-driven development http://www.embedded.com/design/prototyping-and-development/4398723/The-mock-object-approach-to-test-driven-development
Patterns and Practices for Embedded TDD in C and C++, Byran Wills-Heath https://vimeo.com/131644349