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

tests/realtimeGC/tmain.nim

@@ -0,0 +1,54 @@
+discard """
+  cmd: "nim $target --threads:on -d:release -d:useRealtimeGC $options $file"
+  joinable:false
+"""
+
+#[
+was: cmd: "nim $target --debuginfo $options $file"
+these dont' seem needed --debuginfo
+nor these from the previous main.nim.cfg: --app:console
+]#
+
+import times, os, strformat, strutils
+from stdtest/specialpaths import buildDir
+# import threadpool
+
+const runtimeSecs {.intdefine.} = 5
+
+const file = "shared.nim"
+const dllname = buildDir / (DynlibFormat % file)
+
+static:
+  let nim = getCurrentCompilerExe()
+  let (output, exitCode) = gorgeEx(fmt"{nim} c -o:{dllname} --debuginfo --app:lib --threads:on -d:release -d:useRealtimeGC {file}")
+  doAssert exitCode == 0, output
+
+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](runtimeSecs)
+  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()
+
+main()