README.md

Stub return values

# create a double
obj = double()

# specify a return value using `:expect` syntax
allow(obj).to receive(:message) { :value }
allow(obj).to receive(:message).and_return(:value)

# specify a return value using `:should` syntax
obj.stub(:message) { :value }
obj.stub(:message => :value)
obj.stub(:message).and_return(:value)

These forms are somewhat interchangeable. The difference is that the block contents are evaluated lazily when the obj receives the message message, whereas the others are evaluated as they are read.

Fake implementation

allow(obj).to receive(:message) do |arg1, arg2|
  # set expectations about the args in this block
  # and/or return  value
end

obj.stub(:message) do |arg1, arg2|
  # set expectations about the args in this block
  # and/or return a value
end

Raising/Throwing

allow(obj).to receive(:message).and_raise("this error")
allow(obj).to receive(:message).and_throw(:this_symbol)

obj.stub(:message).and_raise("this error")
obj.stub(:message).and_throw(:this_symbol)

You can also use the block format:

allow(obj).to receive(:message) { raise "this error" }
allow(obj).to receive(:message) { throw :this_symbol }

obj.stub(:message) { raise "this error" }
obj.stub(:message) { throw :this_symbol }

Argument constraints

Explicit arguments

allow(obj).to receive(:message).with('an argument') { ... }

obj.stub(:message).with('an argument') { ... }
obj.stub(:message).with('more_than', 'one_argument') { ... }

Argument matchers

allow(obj).to receive(:message).with(anything()) { ... }
allow(obj).to receive(:message).with(an_instance_of(Money)) { ... }
allow(obj).to receive(:message).with(hash_including(:a => 'b')) { ... }
allow(obj).to receive(:message).with(array_including(1,2,3)) { ... }
# or
allow(obj).to receive(:message).with(array_including([1,2,3])) { ... }

obj.stub(:message).with(anything()) { ... }
obj.stub(:message).with(an_instance_of(Money)) { ... }
obj.stub(:message).with(hash_including(:a => 'b')) { ... }

Regular expressions

allow(obj).to receive(:message).with(/abc/) { ... }

obj.stub(:message).with(/abc/) { ... }