First of all, spacesuits were not, if you’ll pardon the metaphor, created in a vacuum.
B.F. Goodrich made pressure suits for air pioneer Wiley Post as early as 1934. This was far from a spacesuit, but it helped pave the way. It was tested by simply inflating it to check for leaks.
早在1934年，古德里奇（B.F. Goodrich）就为航空先驱威利邮报（Wiley Post）制造了压力服。虽然这与航天服相去甚远，但却为后者铺平了道路。这件衣服只需简单地对其充气，就可以通过检查是否泄漏来进行测试。
As aircraft ceilings got higher, life support had to keep up. Pressurized cabins were developed, and partial pressure, then whole-body pressure suits.
【 译注：partial pressure suit是指只保护身体某一部分的压力服】
In the late 1940s, Strato Equipment Company made the first full pressure flight suit, G-suit, and high altitude heated garments. David Clark started making more advanced flight suits for the military. Stratolab flew with Navy funding, carrying pressurized gondolas on some flights, and in others, open gondolas in which men wore only the Navy MC-3 partial pressure suit and thermal protective gear well into the stratosphere.
在1940年代后期，Strato Equipment Company制造了第一套全压飞行服，G-suit和高海拔热保护的服装。大卫·克拉克（David Clark）开始为军人生产更高级的飞行服。 Stratolab在海军的资助下飞行，在某些航班上携带加压的吊船，而在另一些情况下，则是敞开的吊船，其中的人只穿了海军MC-3部分压力服和热保护装置进入平流层。
By the time the NACA was transformed into NASA in 1958, it had a long history helping military and civilian contractors develop high altitude hardware of all types, and had already been long involved in the development of high altitude suits.
Men flying high performance aircraft to the edge of space (as in the X-15 and SR-71, among others) needed suits that would protect them to the edge of space and still allow them to control their craft if its pressurization failed.
By the time of the Mercury program, the Navy Mark IV full pressure suit was the workhorse of military high flying. It was not what we consider a proper spacesuit today, but provided a sufficient atmosphere and sufficient mobility under pressure to permit the occupant to continue flight for the time needed to recover from an emergency. It had been tested in altitude chambers and in numerous flights and accidents in America’s aggressive flight test programs.
When NASA needed a suit for astronauts in the Mercury program, it didn’t have to think very long before buying the Mark-IV. It met all the requirements for an experimental space capsule with no possibility of EVA—except one: They painted it with the same aluminum paint used in fire suits of the time, in case of fires on the pad. Then they tested to make sure it could meet other requirements they thought might come up, like allowing a man to crawl through an airlock in a tight space:
当NASA在水星计划中需要宇航员穿这种服装时，购买Mark-IV无需花费很长时间。如果不考虑太空行走的话， Mark-IV 简直满足了在实验太空舱里所需要的一切——除了一个：他们还需要在 Mark-IV 上使用了与当时的消防服相同的铝漆进行涂漆，以防在垫子上起火。然后他们进行了测试，以确保它可以满足他们认为可能会出现的其他要求，例如允许一个人在狭窄的空间中爬过气闸：
Finally, they put a standard-size astronaut in the suit, strapped him to a chair, and had him push a set of sliding rulers to determine his range of motion. Instruments and stowage were designed around the suit.
The first Gemini flights carried on using modified high altitude suits, and the ACES suits worn by American astronauts during launch throughout most of the Shuttle era and today are still just military high-altitude suits, in International Orange to aid in search and rescue.
Later Gemini and Apollo missions, however, required more sophistication. They needed a suit that could reflect sunlight and reject excess body heat into the vacuum. They needed to bend at the waist. They needed constant volume joints so they’d have less tendency to balloon under inflation. When Gene Cernan on Gemini 9A performed an EVA to retrieve a maneuvering unit stowed behind the capsule, he ended up with gallons of sweat sloshing around in his suit. They needed to remove the moisture generated by a man doing work.
Planning and training had to improve, but so did the suits. The Apollo A7-L worn on lunar missions was the beneficiary of all prior work. It was tested in vacuum chambers:
It was tested in a giant Space Environment Simulation Lab in which the thermal conditions of space were simulated by means of heat lamps and liquid nitrogen cooled chamber walls:
The suits were tested by means of special harnesses supported from an overhead gantry to ensure the inflated suit would offer sufficient flexibility for an astronaut to walk, carry out tasks, and recover from a fall in lunar gravity:
They were tested to make sure they could get onto the ladder and up to the LM:
They were tested to make sure a man wearing one under pressure could squeeze through the hatches:
They were tested in zero-g aboard a KC-135:
In short, the way you know a piece of life support gear is going to work ahead of time, is by testing it progressively, under controlled conditions, ahead of time.