Embedded systems are used in a wide variety of applications (e.g., automotive, agricultural, home security, industrial, medical, military, and aerospace) due to their small size, low-energy consumption, and the ability to control real-time peripheral devices precisely. These systems, however, are different from each other in many aspects: processors, memory size, develop applications/OS, hardware interfaces, and software loading methods. Unit testing is a fundamental part of software development and the lowest level of software testing, as it tests individual or groups of functions, methods, and classes, to increase confidence that the developed software satisfies both software specifications and user requirements. Although hundreds of unit testing frameworks exist, none of them address the diverse properties of real-time embedded platforms. This inspires us to introduce XEUnit, a cross-platform unit testing framework for real-time embedded systems. To address the time constraints in real-time embedded systems, we evaluate the impact of runtime overhead from traditional instrumentation through a case study of time-sensitive algorithms.