Get code coverage working

docs/developing.md

@@ -4,7 +4,7 @@
 You need to ensure you have the following tools installed:
 
 * [Docker](https://www.docker.com/)
-* [Go](https://golang.org/)
+* [Go](https://golang.org/) - only needed for running the tests
 * [Glide](https://glide.sh/)
 * [dep](https://github.com/golang/dep) (official Go dependency management tool)
 * make
@@ -21,10 +21,27 @@ There are three main sets of tests:
 ### Running the tests
 The unit and Docker tests can be run locally.  For example:
 
-```bash
+```
 make test-devserver
 ```
 
+or:
+
+```
+make test-advancedserver
+```
+
+### Running the tests with code coverage
+You can produce code coverage results from the Docker tests by running the following:
+
+```
+make build-advancedserver-cover
+make test-advancedserver-cover
+```
+
+In order to generate code coverage metrics from the Docker tests, the build step creates a new Docker image with an instrumented version of the code.  Each test is then run individually, producing a coverage report each under `test/docker/coverage/`.  These individual reports are then combined.  The combined report is written to the `coverage` directory. 
+
+
 ### Running the Kubernetes tests
 
 For the Kubernetes tests, you need to have built the Docker image, and pushed it to the registry used by your Kubernetes cluster.  Most of the configuration used by the tests is picked up from your `kubectl` configuration, but you will typically need to specify the image details.  For example: