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More about adding a collaboratoryield matchers
There are four related matchers that allow you to specify whether
or not a method yields, how many times it yields, whether or not
it yields with arguments, and what those arguments are.
yield_control
matches if the method-under-test yields, regardless of whether or not arguments are yielded.yield_with_args
matches if the method-under-test yields with arguments. If arguments are provided to this matcher, it will only pass if the actual yielded arguments match the expected ones using===
or==
.yield_with_no_args
matches if the method-under-test yields with no arguments.yield_successive_args
is designed for iterators, and will match if the method-under-test yields the same number of times as arguments passed to this matcher, and all actual yielded arguments match the expected ones using===
or==
.
Note: your expect block must accept an argument that is then passed on to
the method-under-test as a block. This acts as a "probe" that allows the matcher
to detect whether or not your method yields, and, if so, how many times and what
the yielded arguments are.
- Background
-
- Given
-
a file named "my_class.rb" with:
class MyClass def self.yield_once_with(*args) yield *args end def self.raw_yield yield end def self.dont_yield end end
- Scenarios
-
- yield_control matcher
- yield_with_args matcher
- yield_with_no_args matcher
- yield_successive_args matcher
- yield_control matcher
-
- Given
-
a file named "yield_control_spec.rb" with:
require './my_class' describe "yield_control matcher" do specify { expect { |b| MyClass.yield_once_with(1, &b) }.to yield_control } specify { expect { |b| MyClass.dont_yield(&b) }.not_to yield_control } # deliberate failures specify { expect { |b| MyClass.yield_once_with(1, &b) }.not_to yield_control } specify { expect { |b| MyClass.dont_yield(&b) }.to yield_control } end
- When
-
I run
rspec yield_control_spec.rb
- Then
-
the output should contain all of these:
4 examples, 2 failures expected given block to yield control expected given block not to yield control
- yield_with_args matcher
-
- Given
-
a file named "yield_with_args_spec.rb" with:
require './my_class' describe "yield_with_args matcher" do specify { expect { |b| MyClass.yield_once_with("foo", &b) }.to yield_with_args } specify { expect { |b| MyClass.yield_once_with("foo", &b) }.to yield_with_args("foo") } specify { expect { |b| MyClass.yield_once_with("foo", &b) }.to yield_with_args(String) } specify { expect { |b| MyClass.yield_once_with("foo", &b) }.to yield_with_args(/oo/) } specify { expect { |b| MyClass.yield_once_with("foo", "bar", &b) }.to yield_with_args("foo", "bar") } specify { expect { |b| MyClass.yield_once_with("foo", "bar", &b) }.to yield_with_args(String, String) } specify { expect { |b| MyClass.yield_once_with("foo", "bar", &b) }.to yield_with_args(/fo/, /ar/) } specify { expect { |b| MyClass.yield_once_with("foo", "bar", &b) }.not_to yield_with_args(17, "baz") } # deliberate failures specify { expect { |b| MyClass.yield_once_with("foo", &b) }.not_to yield_with_args } specify { expect { |b| MyClass.yield_once_with("foo", &b) }.not_to yield_with_args("foo") } specify { expect { |b| MyClass.yield_once_with("foo", &b) }.not_to yield_with_args(String) } specify { expect { |b| MyClass.yield_once_with("foo", &b) }.not_to yield_with_args(/oo/) } specify { expect { |b| MyClass.yield_once_with("foo", "bar", &b) }.not_to yield_with_args("foo", "bar") } specify { expect { |b| MyClass.yield_once_with("foo", "bar", &b) }.to yield_with_args(17, "baz") } end
- When
-
I run
rspec yield_with_args_spec.rb
- Then
-
the output should contain all of these:
14 examples, 6 failures expected given block not to yield with arguments, but did expected given block not to yield with arguments, but yielded with expected arguments expected given block to yield with arguments, but yielded with unexpected arguments
- yield_with_no_args matcher
-
- Given
-
a file named "yield_with_no_args_spec.rb" with:
require './my_class' describe "yield_with_no_args matcher" do specify { expect { |b| MyClass.raw_yield(&b) }.to yield_with_no_args } specify { expect { |b| MyClass.dont_yield(&b) }.not_to yield_with_no_args } specify { expect { |b| MyClass.yield_once_with("a", &b) }.not_to yield_with_no_args } # deliberate failures specify { expect { |b| MyClass.raw_yield(&b) }.not_to yield_with_no_args } specify { expect { |b| MyClass.dont_yield(&b) }.to yield_with_no_args } specify { expect { |b| MyClass.yield_once_with("a", &b) }.to yield_with_no_args } end
- When
-
I run
rspec yield_with_no_args_spec.rb
- Then
-
the output should contain all of these:
6 examples, 3 failures expected given block not to yield with no arguments, but did expected given block to yield with no arguments, but did not yield expected given block to yield with no arguments, but yielded with arguments: ["a"]
- yield_successive_args matcher
-
- Given
-
a file named "yield_successive_args_spec.rb" with:
def array [1, 2, 3] end def array_of_tuples [[:a, :b], [:c, :d]] end describe "yield_successive_args matcher" do specify { expect { |b| array.each(&b) }.to yield_successive_args(1, 2, 3) } specify { expect { |b| array_of_tuples.each(&b) }.to yield_successive_args([:a, :b], [:c, :d]) } specify { expect { |b| array.each(&b) }.to yield_successive_args(Fixnum, Fixnum, Fixnum) } specify { expect { |b| array.each(&b) }.not_to yield_successive_args(1, 2) } # deliberate failures specify { expect { |b| array.each(&b) }.not_to yield_successive_args(1, 2, 3) } specify { expect { |b| array_of_tuples.each(&b) }.not_to yield_successive_args([:a, :b], [:c, :d]) } specify { expect { |b| array.each(&b) }.not_to yield_successive_args(Fixnum, Fixnum, Fixnum) } specify { expect { |b| array.each(&b) }.to yield_successive_args(1, 2) } end
- When
-
I run
rspec yield_successive_args_spec.rb
- Then
-
the output should contain all of these:
8 examples, 4 failures expected given block not to yield successively with arguments, but yielded with expected arguments expected given block to yield successively with arguments, but yielded with unexpected arguments
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