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RSpec 3 Expectations Cheat Sheet by

Setting expectations in RSpec 3 specs

nil, boolean, equality, type, regex matchers

expect(user).to be_nil

expect( be_truthy
expect( be_falsey

expect( eq("foo")

expect(user).to be_a(FooApp::User)
expect(arr).to be_an(Array)

expect( match(/foo/)
Using not_to instead of to reverses the condition.

Collection matchers

expect([1, 2, 3]).to include(2)

expect(request.headers).to include("X-Foo" => "bar", "X-Baz" => "qux")
expect(request.headers).to have_key("X-Foo")

expect([1, 2, 3]).to all(be_a(Fixnum))

Message expect­ations

expect(FooClass).to receive(:bar).and_return(:baz)
expect(foo).to receive(:bar).and_return(:baz)

expect(foo).to receive(:bar).with(:qux) { }

# equivalent to previous example
allow(foo).to receive(:bar) { }
expect(foo).to have_received(:bar).with(:qux)

# use sparingly :)
expect_any_instance_of(FooClass).to receive(:bar) { true }
expect will fail if the message is not received. allow is a relaxed version and will not fail.


expect { Foo.find(-1) }.to raise_error(ActiveResource::ResourceNotFound)
expect { Foo.find(1) }.not_to raise_error

Rails models

expect(foo).to be_valid

expect(bar).not_to be_valid
expect(bar.errors.messages).to have_key(:baz)

Rails contro­llers and routing

get :index
expect(response).to render_template("index")

# if routes.rb contains
get "/foo" => "foo#method"
# then test it with
expect(get("/foo?bar=baz")).to route_to(controller: "foo", action: "method", bar: "baz")

Rails views

assign(:foo, stub_model(Foo, bar: "baz"))
expect(rendered).to match(/baz/)


expect(foo).to respond_to(:bar)


Define a memoized function to run at the start of each example
let(:baz) { double­(Baz, qux: "­quu­x") }

Now, you can say
allow(­foo).to receiv­e(:­bar­).a­nd_­ret­urn­(baz)

and if you reuse baz in your test, you can be sure it's the same thing.


Thank you, Mike! Very helpful.

Haha I'm not sure why I thought your name is Mike ;). First thing in the morning...

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