;doc: contributing: kent beck tests properties

[ci skip]

CONTRIBUTING.md

@@ -673,6 +673,24 @@ About testing in the hledger project, as of 201809.
 
 ### Kinds of tests
 
+<div style="margin:1em 2em; font-style:italic;">
+"Here, then, is a list of properties of tests. Not all tests need to exhibit all properties. However, no property should be given up without receiving a property of greater value in return.
+
+- Isolated — tests should return the same results regardless of the order in which they are run.
+- Composable — if tests are isolated, then I can run 1 or 10 or 100 or 1,000,000 and get the same results.
+- Fast — tests should run quickly.
+- Inspiring — passing the tests should inspire confidence
+- Writable — tests should be cheap to write relative to the cost of the code being tested.
+- Readable — tests should be comprehensible for reader, invoking the motivation for writing this particular test.
+- Behavioral — tests should be sensitive to changes in the behavior of the code under test. If the behavior changes, the test result should change.
+- Structure-insensitive — tests should not change their result if the structure of the code changes.
+- Automated — tests should run without human intervention.
+- Specific — if a test fails, the cause of the failure should be obvious.
+- Deterministic — if nothing changes, the test result shouldn’t change.
+- Predictive — if the tests all pass, then the code under test should be suitable for production."
+--[Kent Beck](https://medium.com/@kentbeck_7670/test-desiderata-94150638a4b3)
+</div>
+
 1.  Unit tests
 
     Unit tests exercise small chunks of functionality. In hledger, that