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Project: RSpec Expectations 2.13

Publisher: RSpec

expect change

Expect the execution of a block of code to change the state of an object.

Background
Given
a file named "lib/counter.rb" with: 
class Counter
  class << self
    def increment
      @count ||= 0
      @count += 1
    end
    
    def count
      @count ||= 0
    end
  end
end
Scenarios
expect change
Given
a file named "spec/example_spec.rb" with: 
require "counter"

describe Counter, "#increment" do
  it "should increment the count" do
    expect { Counter.increment }.to change{Counter.count}.from(0).to(1)
  end

  # deliberate failure
  it "should increment the count by 2" do
    expect { Counter.increment }.to change{Counter.count}.by(2)
  end
end
When
I run rspec spec/example_spec.rb
Then
the output should contain "1 failure"
Then
the output should contain "should have been changed by 2, but was changed by 1"
expect no change
Given
a file named "spec/example_spec.rb" with: 
require "counter"

describe Counter, "#increment" do
  it "should not increment the count by 1 (using to_not)" do
    expect { Counter.increment }.to_not change{Counter.count}
  end

  it "should not increment the count by 1 (using not_to)" do
    expect { Counter.increment }.not_to change{Counter.count}
  end
end
When
I run rspec spec/example_spec.rb
Then
the output should contain "2 failures"
Then
the output should contain "should not have changed, but did change from 1 to 2"

Last published over 7 years ago by myronmarston.