Update testing doc

Signed-off-by: Daniel Nephin <dnephin@docker.com>
(cherry picked from commit 58de6277821698a2f97d1a0c83664ab34ff2e8d8)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

components/engine/TESTING.md

@@ -8,11 +8,11 @@ questions you may have as an aspiring Moby contributor.
 Moby has two test suites (and one legacy test suite):
 
 * Unit tests - use standard `go test` and
-  [testify](https://github.com/stretchr/testify) assertions. They are located in
+  [gotestyourself/assert](https://godoc.org/github.com/gotestyourself/gotestyourself/assert) assertions. They are located in
   the package they test. Unit tests should be fast and test only their own 
   package.
 * API integration tests - use standard `go test` and
-  [testify](https://github.com/stretchr/testify) assertions. They are located in
+  [gotestyourself/assert](https://godoc.org/github.com/gotestyourself/gotestyourself/assert) assertions. They are located in
   `./integration/<component>` directories, where `component` is: container,
   image, volume, etc. These tests perform HTTP requests to an API endpoint and
   check the HTTP response and daemon state after the call.