/usr/share/doc/ruby-rspec-expectations/features/built_in_matchers/change.feature is in ruby-rspec-expectations 3.4.0c3e0m1s1-1ubuntu1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 | Feature: `change` matcher
The `change` matcher is used to specify that a block of code changes some mutable state.
You can specify what will change using either of two forms:
* `expect { do_something }.to change(object, :attribute)`
* `expect { do_something }.to change { object.attribute }`
You can further qualify the change by chaining `from` and/or `to` or one of `by`, `by_at_most`,
`by_at_least`.
Background:
Given a file named "lib/counter.rb" with:
"""ruby
class Counter
class << self
def increment
@count ||= 0
@count += 1
end
def count
@count ||= 0
end
end
end
"""
Scenario: expect change
Given a file named "spec/example_spec.rb" with:
"""ruby
require "counter"
RSpec.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 "expected result to have changed by 2, but was changed by 1"
Scenario: expect no change
Given a file named "spec/example_spec.rb" with:
"""ruby
require "counter"
RSpec.describe Counter, "#increment" do
it "should not increment the count by 1 (using not_to)" do
expect { Counter.increment }.not_to change{Counter.count}
end
it "should not increment the count by 1 (using to_not)" do
expect { Counter.increment }.to_not 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 "expected result not to have changed, but did change from 1 to 2"
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