testing-bites

RSpec Testing writing process

Write a test for:

• All branches of if statement
• Fringe examples for conditionals e.g. numerical limits
• Each part of conditional e.g. <1> && <2> - write tests for the whole statement, for when only <1> == true and when <2> == true

Tip: Can add bugs to the code to test the tests after they've been written

RSpec syntax

require 'add_five' # We have to require the file with our code in first.

# Then we set up a test suite — a group of tests.
# We use this string to describe the unit of code we're testing
RSpec.describe "add_five method" do

  # Next, we create a single test example.
  # We use the string here to describe what the example is.
  it "adds 5 to 3 to return 8" do
    # We run the method with an example argument 3
    result = add_five(3)

    # And then expect (assert) that in this example it should return 8
    expect(result).to eq 8

    # RSpec will run this example, and if this example doesn't work like you
    # said it would, the test will fail.
  end

  # We can put more test examples here...
end

# But we only have one test suite per file.

Alternatively, could use referental transparency for expect statement:

describe 'fizzbuzz' do
  it 'returns "fizz" when passed 3' do
    expect(fizzbuzz(3)).to eq 'fizz'
  end

RSpec for Classes

Testing classes is fundamentally similar to testing methods. However, classes perform a different job to methods. Instead of taking some arguments and giving a return value like a method, classes look after some data (state) with a common group of methods (behaviour).

Rather than calling one method and check the return value, our example involves calling a number of methods that exercise the intended behaviour of the class.

RSpec for errors

1. We use expect { ... } with curly braces, not parentheses.
2. We put the code that throws the error inside the braces. This, combined with difference 1, 'wraps' this code in a special environment that means RSpec can 'catch' the error.
3. We use raise_error instead of eq (equal).

The keywords raise_error and eq are both kinds of 'matcher'. RSpec supports many matchers. You don't need to know very many of them but they can be interesting to look up.

Example:

# /lib/password_checker.rb
class PasswordChecker
  def check(password)
    if password.length >= 8
      return true
    else
      fail "Invalid password, must be 8+ characters."
    end
  end
end

# /lib/password_checker_spec.rb
it "Password length is less than 8 characters" do
    password = PasswordChecker.new
    expect { password.check("1234567") }.to raise_error "Invalid password, must be 8+ characters."
  end