add conditional for running tests in check stage

memcached.spec

@@ -2,6 +2,7 @@
 %define groupname  memcached
 %bcond_without sasl
 %bcond_with seccomp
+%bcond_with tests
 %global selinuxtype	targeted
 %global selinuxmoduletype	contrib
 %global selinuxmodulename	memcached
@@ -76,8 +77,8 @@ make
 popd
 
 %check
-# disable testing as it is unreliable on build systems
-exit 0
+# tests are disabled by default as they are unreliable on build systems
+%{!?with_tests: exit 0}
 
 # whitespace tests fail locally on fedpkg systems now that they use git
 rm -f t/whitespace.t