become and become_true matchers --- use instead of Capybara's wait_until

gistfile1.rb

# Matchers that will wait for a value to change.                                                                                                                                                                                                                              

# Ex. expect { email.reload.delivered? }.to become_true
RSpec::Matchers.define :become_true do
  match do |block|
    begin
      Timeout.timeout(Capybara.default_wait_time) do
        sleep(0.1) until value = block.call
        value
      end 
    rescue TimeoutError
      false
    end 
  end 
end

RSpec::Matchers.define :become_false do
  match do |block|
    begin
      Timeout.timeout(Capybara.default_wait_time) do
        sleep(0.1) until value = !block.call
        value
      end 
    rescue TimeoutError
      false
    end 
  end 
end

# Ex. expect { page.current_url }.to become( '/#/something_or_other' )
RSpec::Matchers.define :become do |expected|
  match do |block|
    begin
      Timeout.timeout(Capybara.default_wait_time) do
        sleep(0.1) until value = ( block.call == expected )
        value
      end 
    rescue TimeoutError
      false
    end 
  end 
end

@wardpenney use a block:

expect { font_color_is_good }.to become_true

n.b. you also have to add the line:

supports_block_expectations

to each matcher for RSpec 3.0+