1. Testing in Erlang

2. Different testing tools EUnit (standard lightweight xUnit solution for Erlang) Common Test (OTP based distributed testing tool) Qucik Check (property based testing tool)

3. A simple problem (deleting from a list) 4>lists:delete(2,[1,2,3]). [1,3] 5>lists:delete(4,[1,2,3]). [1,2,3] We should write a test for delete like this: delete_present_test()-> lists:delete(2,[1,2,3])==[1,3]. delete_absent_test()-> lists:delete(4,[1,2,3])==[1,2,3].

4. Problems with xUnit style solution Lots of work to create “good” tests and various test cases The code as good as your tests Can’t create and validate with formal specification

5. What other solution is possible We’d like to generalise our tests We’d like to generate or run different cases automatically We’d like to avoid the “human failure” from the system (if it is even possible) We’d like to write something like this: prop_delete(I,L)-> notlists:member(I,lists:delete(I,L)).

6. QuickCheck is the solution With QuickCheck we can test our property automatically in many cases without the effort of specifying each case manually So we can write QuickCheck property like this: prop_delete()-> ?FORALL({I,L},{int(),list(int())}, notlists:member(I,lists:delete(I,L))).

7. Test data generators Instead of the logically meaning QuickCheck interprets the expression as a data generator int() is a generator of random integers list(int()) is a generator of random lists containing integers {int(), list(int)} produces pairs of integer and a list of integers ?FORALL binds {I,L} to the pattern {int(), list(int)}

8. Running the test eqc:quickcheck(examples:prop_delete()). Works fine! eqc:quickcheck(eqc:numtests(1000,examples: prop_delete())). Fails… Diagnosis and shrinking

9. Conditional properties ?IMPLIES prop_delete()-> ?FORALL({I,L},{int(),list(int())}, ?IMPLIES(no_duplicates(L), not lists:member(I,lists:delete(I,L)))). no_duplicates(L)- >lists:usort(L)==lists:sort(L).

10. Custom generators We can create our own generators ulist(Elem)-> ?LET(L,list(Elem), lists:usort(L)).