The PocketQube is an emerging satellite class, which pushes the miniaturization of space technology beyond the well-established CubeSats, promising rapid design-to-orbit cycles while lowering the cost of accessing space. A showstopper in the success story of nano- and picosatellites are their high mission failure rates. Environmental testing before flight is an effective means to identify design flaws and workmanship errors, and thus improve the chances of mission success. However, inefficiencies in the design process, low-budgets, and stringent schedule requirements often motivate small satellite developers to postpone environmental testing towards the end of the design lifecycle, where recovering for design flaws is inefficient. The project circumstance of nano- and picosatellite missions require, therefore, cost- and time-effective test strategies that facilitate early design evaluation. This research proposes and implements a thermal screening method for PocketQube subsystems to identify temperature hotspots and verify their compliance against operational hardware limits. Key elements of the test method are a thermal IR temperature scan at ambient conditions and an estimation of the worst-case flight temperature using experimentally derived graphs that describe the vacuum heating of thermal hotspots. The study of subsystem layout options complements the screening method by providing solutions to mitigate hotspot overheating. Moreover, the study proposes to lower the required pressure levels for thermal-vacuum testing of PocketQube subsystems. The analysis shows that, due to the small form factor, pressure levels by four orders of magnitude larger than those used in environmental test standards for larger satellites suffice to maintain the resulting temperature errors below 5K on the hot side of the temperature spectrum. Both the screening method and moderation in vacuum requirements contribute to the development of subsystem test methods that match the needs of small satellite developers.