error instead of echo when testament category is empty; fix realtimeGC (#16162)

tests/realtimeGC/nmain.nim

@@ -1,46 +0,0 @@
-discard """
-  cmd: "nim $target --debuginfo $options $file"
-  output: "Done"
-"""
-
-import times, os, threadpool
-
-const RUNTIME = 15 * 60 # 15 minutes
-
-when defined(windows):
-  const dllname = "./tests/realtimeGC/shared.dll"
-elif defined(macosx):
-  const dllname = "./tests/realtimeGC/libshared.dylib"
-else:
-  const dllname = "./tests/realtimeGC/libshared.so"
-
-proc status() {.importc: "status", dynlib: dllname.}
-proc count() {.importc: "count", dynlib: dllname.}
-proc checkOccupiedMem() {.importc: "checkOccupiedMem", dynlib: dllname.}
-
-proc process() =
-  let startTime = getTime()
-  let runTime = cast[Time](RUNTIME) #
-  var accumTime: Time
-  while accumTime < runTime:
-    for i in 0..10:
-      count()
-    # echo("1. sleeping... ")
-    sleep(500)
-    for i in 0..10:
-      status()
-    # echo("2. sleeping... ")
-    sleep(500)
-    checkOccupiedMem()
-    accumTime = cast[Time]((getTime() - startTime))
-    # echo("--- Minutes left to run: ", int(int(runTime-accumTime)/60))
-
-proc main() =
-  process()
-  # parallel:
-  #   for i in 0..0:
-  #     spawn process()
-  # sync()
-  echo("Done")
-
-main()