update Testing after changes to test coverage

Note that it takes less time to execute, and the old test suites
are not runnable any more, so there is no need to say that they
existed

warn about hypothesis-introduced variability in runtime

README.md

@@ -101,17 +101,18 @@ safer to use. You are looking at the README for this wrapper.
 
 ## Testing
 
-There are four test suites, three for the original Pearson module, and one
-more for the wrapper. To run them all, do this:
+To run the full test suite, do this:
 
     tox -e coverage
 
-On an Intel Core i7 4790K @ 4.0GHz, the combined tests take about 8 minutes to
-run.
+On an Intel Core i7 4790K @ 4.0GHz, the tests take about 150 seconds to execute.
+The test suite uses
+[`hypothesis`](https://github.com/HypothesisWorks/hypothesis) so there is some
+inherent variability in the test suite execution time.
 
-One component of `test_pyecdsa.py` checks compatibility with OpenSSL, by
+One part of `test_pyecdsa.py` checks compatibility with OpenSSL, by
 running the "openssl" CLI tool, make sure it's in your `PATH` if you want
-to test it.
+to test compatibility with it.
 
 ## Security