Add warning a file given to Test contains no tests

lib/test.gi

@@ -419,6 +419,11 @@ InstallGlobalFunction("Test", function(arg)
 
   # split input into GAP input, GAP output and comments
   pf := ParseTestInput(full, opts.ignoreComments);
+
+  # Warn if we have not found any tests in the file
+  if IsEmpty(pf[1]) then
+    Info(InfoWarning, 1, "Test: File does not contain any tests!");
+  fi;
 
   # run the GAP inputs and collect the outputs and the timings
   RunTests(pf, rec(breakOnError := opts.breakOnError, 

tst/testinstall/files/invalidtestfile.txt

@@ -0,0 +1,8 @@
+# This file contains some valid GAP code which is not
+# a valid tst file, to check error reporting.
+#
+# It has a ".txt" extension to avoid it being found by
+# Any code which looks through testinstall for .g or .tst files
+
+x := 3;
+g := SymmetricGroup(5);

tst/testinstall/files/test.tst

@@ -0,0 +1,10 @@
+gap> START_TEST("test.tst");
+gap> dir := DirectoriesLibrary("tst/testinstall/files");;
+gap> Test(Filename(dir,"empty.txt"));
+#I  Test: File does not contain any tests!
+true
+gap> Test(Filename(dir,"invalidtestfile.txt"));
+Error, Invalid data in test file
+gap> Test(Filename(dir, "tinytest.txt"));
+true
+gap> STOP_TEST("test.tst");

tst/testinstall/files/tinytest.txt

@@ -0,0 +1 @@
+gap> 1;;