+Sometimes it's hard to come up with edge cases for tests, or sometimes
+there are so many that it's hard to list them all one by one. Random
+testing is a way to tell the test suite how to generate input and how
+to test that certain conditions always hold. One issue when writing
+random tests is that you can't, usually, test for specific results,
+you have to test that certain relationships hold.
+
+For example, if we had a function which reverses a list, we could
+define a relationship like this:
+
+--------------------------------
+(equalp the-list (reverse (reverse the-list)))
+--------------------------------
+
+or
+
+--------------------------------
+(equalp (length the-list) (length (reverse the-list)))
+--------------------------------
+
+Random tests are defined via `def-test`, but the random part is then
+wrapped in a xref:OP_FOR-ALL[`for-all`] macro which runs its body
+`*num-trials*` times with different inputs: