Module | RSpec::Core::Let::ExampleGroupMethods |
In: |
lib/rspec/core/let.rb
|
Generates a method whose return value is memoized after the first call. Useful for reducing duplication between examples that assign values to the same local variable.
@note `let` can enhance readability when used sparingly (1,2, or
maybe 3 declarations) in any given example group, but that can quickly degrade with overuse. YMMV.
@note `let` uses an `||=` conditional that has the potential to
behave in surprising ways in examples that spawn separate threads, though we have yet to see this in practice. You've been warned.
@example
describe Thing do let(:thing) { Thing.new } it "does something" do # first invocation, executes block, memoizes and returns result thing.do_something # second invocation, returns the memoized value thing.should be_something end end
Just like `let`, except the block is invoked by an implicit `before` hook. This serves a dual purpose of setting up state and providing a memoized reference to that state.
@example
class Thing def self.count @count ||= 0 end def self.count=(val) @count += val end def self.reset_count @count = 0 end def initialize self.class.count += 1 end end describe Thing do after(:each) { Thing.reset_count } context "using let" do let(:thing) { Thing.new } it "is not invoked implicitly" do Thing.count.should eq(0) end it "can be invoked explicitly" do thing Thing.count.should eq(1) end end context "using let!" do let!(:thing) { Thing.new } it "is invoked implicitly" do Thing.count.should eq(1) end it "returns memoized version on first invocation" do thing Thing.count.should eq(1) end end end