With the advent of the 5G era, the capacity of existing single-mode optical fiber communication networks is approaching the Shannon limit, making it increasingly difficult to meet the rapidly growing demand for network bandwidth. To address this challenge, space-division multiplexing (SDM) technologybased on expanding the spatial dimension-has emerged as a promising solution. By multiplexing spatial channels within multimode fibers, few-mode fibers, multi-core fibers, or few-mode multi-core fibers, SDM enables an order-of-magnitude increase in transmission capacity per fiber. Simultaneously, it significantly reduces system footprint and deployment costs through efficient spatial resource utilization. Beyond its transformative role in expanding optical communication capacity, SDM has also introduced new paradigms in multidimensional fiber-optic sensing and catalyzed breakthroughs in high-resolution imaging and system flexibility. However, practical implementation of SDM systems is challenged by mode crosstalk, inter-core crosstalk, and mode-dependent loss—mainly arising from fiber and component fabrication imperfections. These factors can lead to severe inter-channel interference and degradation of overall system performance. To ensure that SDM fibers and devices meet stringent performance requirements, the development of high-precision characterization and testing systems is essential. This paper identifies the key parameters for both SDM fibers and associated devices, and provides a comprehensive review of current mainstream testing techniques, including multi-channel optical time domain reflectometry, spatially and spectrally resolved imaging, fixed analyzer methods, coherent optical frequency domain reflectometry, swept-wavelength interferometry, and off-axis digital holography. Each technique exhibits unique advantages in terms of measurable targets, parameter coverage, and application scenarios. This is the first review to systematically compare the strengths, limitations, and suitability of various SDM testing technologies, offering practical guidance for selecting appropriate testing strategies for SDM devices. Finally, the paper presents an outlook on the future development trends of SDM characterization and testing technologies.