greptest.md

@@ -33,3 +33,9 @@ You can also use different files of test cases.   For example, to test using the
 ```
 python greptest.py -t proptest.xml -d . ../build/bin/icgrep
 ```
+
+When using `greptest.py` in verbose mode, you may see that test cases are often executed with extra command line parameters.   This is a combinatorial testing strategy.   This can be controlled with parameters to greptest.    For more thorough testing you can try the following command.
+
+```
+python greptest.py -v --random_flag_count=3 --tests_per_grepcase=5 ../build/bin/icgrep
+```
\ No newline at end of file