diff --git a/Contributing.md b/Contributing.md
index c587c89..0dfd63f 100644
--- a/Contributing.md
+++ b/Contributing.md
@@ -17,6 +17,13 @@ Before your contributions can be accepted, you must:
 * All source files must end with a newline
 * Line endings: UNIX style (\n)
 
+## Testing
+
+All Pull Requests should, unless impossible/impractical, contain tests for the new functionality.
+
+For a new feature this should be a basic smoke test of the feature plus tests for edge cases and for parameter changes.
+
+For a bug fix there should be at least one test that fails without the fix and passes with it. 
 
 ## Design Principles