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Project: RSpec Expectations 2.14

be_within matcher

Normal equality expectations do not work well for floating point values.
Consider this irb session:

> radius = 3
  => 3
> area_of_circle = radius * radius * Math::PI
  => 28.2743338823081
> area_of_circle == 28.2743338823081
  => false

Instead, you should use the be_within matcher to check that the value
is within a delta of your expected value:

  area_of_circle.should be_within(0.1).of(28.3)

Note that the difference between the actual and expected values must be
smaller than your delta; if it is equal, the matcher will fail.

Scenarios
basic usage
Given
a file named "be_within_matcher_spec.rb" with:
describe 27.5 do
  it { should be_within(0.5).of(27.9) }
  it { should be_within(0.5).of(28.0) }
  it { should be_within(0.5).of(27.1) }
  it { should be_within(0.5).of(27.0) }

  it { should_not be_within(0.5).of(28.1) }
  it { should_not be_within(0.5).of(26.9) }

  # deliberate failures
  it { should_not be_within(0.5).of(28) }
  it { should_not be_within(0.5).of(27) }
  it { should be_within(0.5).of(28.1) }
  it { should be_within(0.5).of(26.9) }
end
When
I run rspec be_within_matcher_spec.rb
Then
the output should contain all of these:
10 examples, 4 failures
expected 27.5 not to be within 0.5 of 28
expected 27.5 not to be within 0.5 of 27
expected 27.5 to be within 0.5 of 28.1
expected 27.5 to be within 0.5 of 26.9

Last published 10 months ago by myronmarston.