runtests: if DISABLED cannot be read, error out

Because then runtests cannot disable the right set of tests and things
will be annoying.

Closes #14411

diff --git a/tests/runtests.pl b/tests/runtests.pl
index a4dc68e1424d2d00189ec62008854b06af6f8a07..19a9445f03aa6ae567e473374d39617a700c31d8 100755 (executable)
--- a/tests/runtests.pl
+++ b/tests/runtests.pl
@@ -2622,6 +2622,10 @@ sub disabledtests {
             }
         }
     }
+    else {
+        print STDERR "Cannot open $file, exiting\n";
+        exit 3;
+    }
 }
 
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