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Several examples how to use Ruby RSpec 3 `be_within` matcher for delta compare
require 'rspec'
require 'time'
require 'active_support/time'
class Foo
def float_range_example
33 * 5 * Math::PI
end
def time_range
Time.now
end
def hash_with_range_value
{
id: 1,
created_at: Time.now,
city: "Banska Bystrica"
}
end
def array_with_range_values
[Time.now, Time.now.midnight, Time.now.midday, 3.days.ago]
end
def array_with_hash_with_range_value
[
{ id: 12, created_at: Time.now },
{ id: 33, created_at: Time.now.midnight }
]
end
end
RSpec.describe(Foo) do
subject { described_class.new }
describe '#float_range_example' do
it do
# if the value is from e.g.DB than this may not be true
#
# expect(subject.float_range_example).to eq(518.3627878423158)
#
# therefore we must define range of value where that float number
# value is acceptable
expect(subject.float_range_example).to be_within(0.01).of(518.3627878423158)
end
end
describe '#time_range' do
context 'in pure Ruby' do
it do
expect(subject.time_range).to be_within(1).of(Time.now)
end
end
context 'in Rails' do
it do
expect(subject.time_range).to be_within(1.second).of(Time.now)
end
end
end
describe '#hash_with_range_value' do
it do
expect(subject.hash_with_range_value).to match({
id: 1,
created_at: be_within(1.second).of(Time.now),
city: /[bB]an/
})
end
end
describe '#array_with_range_values' do
it do
expect(subject.array_with_range_values).to match_array([
be_within(2.seconds).of(Time.now),
be_within(2.seconds).of(Time.now.midnight),
be_within(2.seconds).of(Time.now.midday),
be_within(2.seconds).of(Time.now - 3.days),
])
end
end
describe '#array_with_hash_with_range_value' do
it do
expect(subject.array_with_hash_with_range_value).to match_array([
{ id: 12, created_at: be_within(2.seconds).of(Time.now) },
{ id: 33, created_at: be_within(2.seconds).of(Time.now.midnight) }
])
end
end
end
# Resources
#
# * RSpec version 3.4
# * Ruby 2.3.0
# * https://www.relishapp.com/rspec/rspec-expectations/v/2-8/docs/built-in-matchers/be-within-matcher
@equivalent

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equivalent commented Jun 29, 2016

Full article can be found here => http://www.eq8.eu/blogs/27-rspec-be_within-matcher

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