Let's get this out of the way first: This question is not a duplicate of this earlier question. I'll explain why below.
I'm running the command xcodebuild test -scheme 'ISO8601ForCocoa' SYMROOT=../build, and here's the output:
Executed 16 tests, with 0 failures (0 unexpected) in 0.047 (0.051) seconds profiling: invalid magic number (0x656d6954) profiling: invalid magic number (0x00000000) ** TEST SUCCEEDED **
The person who asked that earlier question got the same error message, but they fixed it by cleaning their build folder.
In my case, cleaning will not help, because I don't have a build folder yet. I still get this error message even on a completely fresh build. In fact, the .gcda and .gcno files are not even created, so there is nothing to clean.
xcodebuild puts build products in $SYMROOT, but stores profile products in $OBJROOT.
If you want to completely confine a build, including all intermediate and ultimate products, to a single directory, you need to set three build settings:
SYMROOT: Build Products Path (ultimate products, such as apps and test bundles)OBJROOT: Intermediate Build Files Path (intermediate products, such as per-module object files—generated by the compiler, read by the linker—and .gcno/.gcda files)SHARED_PRECOMPS_DIR: Precompiled Headers Cache Path (guess)