Francisco Casas (@fcasas) commented about tests/hlsl/strings.shader_test:
+[pixel shader] +float4 main(uniform float4 x) : sv_target
Specifying a uniform doesn't seem necessary for this test.
But if we want to test that its value it is not corrupted for some reason, then we should return it (and probably give it a different value than (0, 0 , 0 ,0).