Testing Your Programs

Bart Massey 2013-10-22

Overview

• Misc notes
• V&V
• Triangle Testing
• Testing Basics
• Advanced Testing

Misc Notes

• Yesterday's CSOD was http://thedailywtf.com/Comments/Deterministic-Programming.aspx.

• Today's CSOD is http://thedailywtf.com/Articles/Unit-Tested.aspx.

• Homework 3 will be up shortly.

V&V

• There are three basic methods of verifying and validating code.

  • Testing
  • Inspection
  • Formal methods

• Inspection and formal methods can also be used to verify and validate other things.

• We will mostly focus on testing and inspection in this class.

A Test Is An Input-Output Pair

• This includes "should fail" negative tests

• How to get correct outputs? (the "effective oracle" problem)

  • Slow but correct code (but few tests)
  • Working backward from output to input
  • "Easy" inputs

Triangle Testing

• From Glenford Myers "The Art of Software Testing"

• Let's write a program printing whether a triangle is scalene, isosceles or equilateral

  • The program should take three numeric arguments
  • It should print the appropriate message after analysis

• Write as many tests as you can think of that might be useful here

• Let's look at an implementation

• Write as many more tests as you can think of

• Now we iterate a bit

Testing Doesn't Work

• Space of possible tests is ridiculously big, like 10^1000

• Tests can only fail

• Test failures usually give minimal insight

• Best that can be hoped for is to test enough cases a user might encounter that the program is known to "kind of" work

Black Box vs White Box

• Black Box: Tests given without knowledge of implementation

• White Box: Use implementation knowledge to construct tests

• Both are valuable

Test Domains

• Idea: Divide input or output space up such that only one representative in each domain need be tested

  • How to draw domain boundaries?
  • There are still a lot
  • Better idea: formal methods plus testing

Testing Kinds

• What should be tested?

  • System (acceptance)
  • Unit
  • Integration
  • Regression

• Integration testing can be

  • bottom-up
  • top-down

Testing Methods

• Random (e.g. "fuzz testing")

• "User Tests"

• Code-driven

• Domain-driven

• Coverage-driven

Coverage Testing

• How much of the program has been tested?

  • All statements?
  • All branches (each way)?
  • All code paths?
  • All data patterns?

• Automated tools (e.g. gcov) exist

• 100% coverage is impossible

• Untested code is broken code

Fault Seeding

• Attempt to find out how good the tests are

• Use SCMS to reliably remove seeded faults (!)

Testing Infrastructure

• Tests need to be maintained with code

• Tests need to be runnable automatically

• Test failures need to be logged as tickets until fixed