RSpec 3 Expectations Cheat Sheet by mpicker0

expect(user).to be_nil

expect(foo.bar?).to be_truthy
expect(foo.bar?).to be_falsey

expect(user.id).to eq("foo")

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

expect(user.id).to match(/foo/)

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))

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

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

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

# use sparingly :)
expect_any_instance_of(FooClass).to receive(:bar) { true }

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

expect(foo).to be_valid

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

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")

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

expect(foo).to respond_to(:bar)