update readme

tests/README.md

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-# Arduino Client for MQTT Test Suite
+## Arduino Client for MQTT Test Suite
+
+This is a regression test suite for the `PubSubClient` library.
+
+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.
+
+## Dependencies
+
+ - Python 2.7+
+ - [INO Tool](http://inotool.org/) - this provides command-line build/upload of Arduino sketches
+
+## Running
+
+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. 
+ 
+   $ python testsuite.py
+
+## What it does
+
+For each example sketch, `sketch.ino`, the suite looks for a matching test case
+`testcases/sketch.py`.
+
+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_`
+ 
+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
+a client and subscribing to topics.
+
+
+## Settings
+
+The file `testcases/settings.py` is used to config the test environment.
+
+ - `server_ip` - the IP address of the broker the client should connect to
+ - `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:
+
+     byte server[] = {
+     byte ip[] = {
+
+