update readme

tests/README.md

@@ -19,7 +19,9 @@ Without a suitable arduino plugged in, the test suite will only check the
 example sketches compile cleanly against the library.
 
 With an arduino plugged in, each sketch that has a corresponding python
-test case is built, uploaded and then the tests run. 
+test case is built, uploaded and then the tests run.
+
+The test suite _does not_ run an MQTT server - it is assumed to be already running.
  
    $ python testsuite.py
 
@@ -31,10 +33,10 @@ For each example sketch, `sketch.ino`, the suite looks for a matching test case
 The test case must follow these conventions:
  - sub-class `unittest.TestCase`
  - provide the class methods `setUpClass` and `tearDownClass` (TODO: make this optional)
- - all test method names must begin with `test_`
+ - all test method names begin with `test_`
  
 The suite will call the `setUpClass` method _before_ uploading the sketch. This
-allows any test setup to be performed before the the sketch runs - such as connecting
+allows any test setup to be performed before the sketch runs - such as connecting
 a client and subscribing to topics.
 
 
@@ -46,11 +48,13 @@ The file `testcases/settings.py` is used to config the test environment.
  - `arduino_ip` - the IP address the arduino should us
 
 Before each sketch is compiled, these values are automatically substituted in. To
-do this, the suite looks for lines that match the following:
+do this, the suite looks for lines that _start_ with the following:
 
      byte server[] = {
      byte ip[] = {
 
+and replaces them with the appropriate values.
+