1. Unit Testing in Ruby
22-Feb-19

2. Programming methodologies
The grim facts:
The majority of large programming projects fail
Projects that succeed are usually full of bugs
Modifying and debugging programs usually introduces yet more bugs
Hence, it is hazardous to modify a “working” program
The time spent maintaining a program far exceeds (10x?) the amount of time it took to write the program
Programming methodologies are attempts to solve these problems by properly organizing programs and/or programmers
The current (and best) methodologies are the “agile” methodologies
“Agile” means writing software that is easily changed
XP (Exteme Programming) is the best known agile methodology
XP tends to work best for small groups of programmers

3. Some ideas from agile programming
There is no “silver bullet,” but agile methodologies are the best we have at present
Most large programming projects fail, so...
“Write the simplest thing that can possibly work.”
Always have a working version, no matter how little it does
Never add a feature until all known bugs have been fixed
Any code that hasn’t been tested is assumed to be wrong
Have tests for all code, and keep it up to date
Run tests frequently—very frequently
Tests must be trivially easy to run, or you won’t bother running them

4. Test suites
Obviously you have to test your code to get it working in the first place
You can do ad hoc testing (running whatever tests occur to you at the moment), or
You can build a test suite (a thorough set of tests that can be run at any time)
Disadvantages of a test suite
It’s a lot of extra programming
This is true, but use of a good test framework can help quite a bit
You don’t have time to do all that extra work
False—Experiments repeatedly show that test suites reduce debugging time more than the amount spent building the test suite
Advantages of a test suite
Reduces total number of bugs in delivered code
Makes code much more maintainable and refactorable
This is a huge win for programs that get actual use!

5. XP approach to testing In the Extreme Programming approach,
Tests are written before the code itself
If code has no automated test case, it is assumed not to work
A test framework is used so that automated testing can be done after every small change to the code
This may be as often as every 5 or 10 minutes
If a bug is found after development, a test is created to keep the bug from coming back
Consequences
Fewer bugs
More maintainable code
Continuous integration—During development, the program always works—it may not do everything required, but what it does, it does right

6. Terminology
A test fixture sets up the data (both objects and primitives) that are needed to run tests
Example: If you are testing code that updates an employee record, you need an employee record to test it on
A unit test is a test of a single class
A test case tests the response of a single method to a particular set of inputs
A test suite is a collection of test cases
A test runner is software that runs tests and reports results
An integration test is a test of how well classes work together
JUnit provides some limited support for integration tests

7. Once more, in pictures test runner test fixture
test suite
test runner
another unit test
test case (for one method)
another test case
A unit test tests the methods in a single class
A test case tests (insofar as possible) a single method
You can have multiple test cases for a single method
A test suite combines unit tests
The test fixture provides software support for all this
The test runner runs unit tests or an entire test suite
Integration testing (testing that it all works together) is not well supported by JUnit
another unit test
another test case
unit test (for one class)
test case (for one method)
another test case
test fixture

8. The test runner The test runner runs all your tests
If they all succeed, you get a green bar
If any fail, you get a red bar and links to the tests that failed

9. How not to write a unit test
Unit tests must be fast and easy to run—or you won’t run them
The only output you should need to look at, in order to see that all tests passed, at is the green bar
Of course, if you get a red bar, you need to explore further
Don’t do any output from your unit tests!
Ideally, the methods you are testing should not do any output
In most well-written programs, there is a separation of concerns—methods either compute or do output, but not both
It is possible to write unit tests for methods that do output, but that is a slightly advanced topic I won’t cover here

10. How to write a unit test class
A unit test class is a class you write that extends Test::Unit::TestCase
You will need the line require 'test/unit'
Your test class will inherit the following methods:
def setup
This a method that will be called before each of your test methods
Typically, you will override this method and use it to assign values to some instance variables you need in testing
def teardown()
This a method that will be called after each of your test methods
Typically you will just ignore this method, unless you need to close files
You will also write any number of test methods, all of which have the form def test_Something
Something is usually, but not necessarily, the name of the method you want to test
Inside each test method, you will do some computations and call one or more assert methods to test the results

11. Available assertion methods
assert boolean
assert_equal expected, actual
Uses ==
assert_same expected, actual
Uses equal?
assert_not_equal expected, actual
assert_not_same expected, actual
assert nil object
assert not_nil object
assert_block block
All these methods can take an additional message argument
This is not a complete listing of the assert methods
The first two methods are by far the most commonly used

12. Structure of a unit test
require "test/unit" require "file_to_be_tested" class CountTest < Test::Unit::TestCase def setup # Perform initializations here end def test_some_method # Tests go here end def teardown # Release any resources (usually not needed) end end

13. Testing for exceptions
Methods should throw exceptions if they are called incorrectly
You can test whether a method throws an exception when it ought to
def test_exceptions begin # Call the method that should throw an exception rescue Exception # or you can test for specific exceptions return # The exception happened, so the test passes end flunk end
Ruby also has assert_raise and assert_throws methods, but I haven’t been able to make them work

14. A complete example class Counter attr_reader :value
def initialize @value = 0 end
def increment *n if n == [ ] @value += else @value += n[0] end end
def reset @value = 0 end end

15. The test class, part 1
require "test/unit" require "counter" class CountTest < Test::Unit::TestCase
def setup @c = Counter.new end
def test_increment_with_no_args assert_equal @c.increment assert_equal @c.increment assert_equal end
def test_increment_with_arg assert_equal @c.increment assert_equal @c.increment assert_equal end
def test_reset @c.increment @c.increment 10 > @c.reset end

16. The test class, part 2
def test_exceptions begin @c.increment 'four' return rescue Exception end flunk end end # of the test class

17. Test suites A test suite is a collection of unit tests
In Ruby, all you have to do is require each test file
Example suite (containing just the one unit test:
require 'ruby_tests‘
Note: In RadRails, running a test suite produces only text output

18. Test-Driven Development (TDD)
It is difficult to add unit tests to an existing program
The program probably wasn’t written with testing in mind
It’s actually better to write the tests before writing the code you want to test
This seems backward, but it really does work better:
When tests are written first, you have a clearer idea what to do when you write the methods
Because the tests are written first, the methods are necessarily written to be testable
Writing tests first encourages you to write simpler, single-purpose methods
Because the methods will be called from more than one environment (the “real” one, plus your test class), they tend to be more independent of the environment

19. Recommended approach Write a test for some method you intend to write
If the method is fairly complex, test only the simplest case
Write a stub for the method
Run the test and make sure it fails
Replace the stub with code
Write just enough code to pass the tests
Run the test
If it fails, debug the method (or maybe debug the test); repeat until the test passes
If the method needs to do more, or handle more complex situations, add the tests for these first, and go back to step 3

20. The End
If you don't unit test then you aren't a software engineer, you are a typist who understands a programming language.
--Moses Jones
1. Never underestimate the power of one little test.
2. There is no such thing as a dumb test.
3. Your tests can often find problems where you're not expecting them.
4. Test that everything you say happens actually does happen.
5. If it's worth documenting, it's worth testing.
--Andy Lester