CMSC330

Test: routine that checks the operation of your code

Why Test

• Save Time
• Allows for Expansion
• Increases Trust
• Helps Collaboration

Things to Test

• Branch Coverage
• Statement Coverage

Types of Tests

• White Box
• Black Box
• Isolated
• Integration
• Functional

Unit test: testing units of a program

let rec three_in_a_row lst = match lst with
[] -> false
|[_] -> false
|[_;_] -> false
|[a;b;c] -> a = b && b = c
|a::b::c::t if a = b && b = c then true else three_in_a_row t;;
          

We can test in utop:

three_in_a_row [1;2;2;2;3;4]
three_in_a_row [1;2;2;3;2;4]
three_in_a_row [1]
          

We can test in utop:

three_in_a_row [1;2;2;2;3;4]
three_in_a_row [1;2;2;3;2;4]
three_in_a_row [1]
          

Or use a Testing Framework (OUnit, JUnit, Minitest,pytest,cargo)

let tests = "Testing for tiar" >::: [
  "valid" >:: (fun _ -> assert_equal true (three_in_a_row [1;2;2;2;3;4]));
  "seperated" >:: (fun _ -> assert_equal false (three_in_a_row [1;2;2;3;2;4]));
  "not enough" >:: (fun _ -> assert_equal false (three_in_a_row [1]));
  ]
          

let tests = "Testing for tiar" >::: [
  "valid" >:: (fun _ -> assert_equal true (three_in_a_row [1;2;2;2;3;4]));
  "seperated" >:: (fun _ -> assert_equal false (three_in_a_row [1;2;2;3;2;4]));
  "not enough" >:: (fun _ -> assert_equal false (three_in_a_row [1]));
  ]
          

There are some limitations

• Need to think of things to check
• Writing becomes O(n)
• Edge Cases hard to think of

Enter Property Based Testing

Enter Property Based Testing

Property Based Testing (PBT): testing if code satisfies properties

Property: Something we expect to be true

Property: Something we expect to be true

Some examples

• Even integers are divisible by 2
• Reversing a list twice should be have no effect
• Adding an element to a list, then looking up that element should succeed
• Deleting an element to a list, then looking up that element should fail
• Sum of a list should be >= largest element
• A sorted list should have smallest value at index 0

• Even integers are divisible by 2

Once we have a property, we need to express our property in terms of code

fun x -> is_even (x*2) = true 
          

Then use a pbt framework (like qcheck)

let even_test = Test.make (int) (fun x -> is_even (x*2) = true) in
QCheck_runner.run_tests [even_test]
          

Limitations on PBT

• Not everything can be a property
• Conversion of property to code can be incorrect
• Thinking of properties is also hard