ruby-simple-navigation: FTBFS: undefined method `stub!'

Imported from Debian bug http://bugs.debian.org/795116:

Source: ruby-simple-navigation
Version: 3.11.0-1
Severity: serious
Justification: fails to build from source
Tags: sid stretch
User: <email address hidden>
Usertags: ftbfs
X-Debbugs-CC: <email address hidden>

Dear Maintainer,

The package fails to build:

Failures:

  1) SimpleNavigation::Adapters::Padrino link_to should delegate to context
     Failure/Error: SimpleNavigation::Adapters::Padrino.new(@context)
     NoMethodError:
       undefined method `request' for #<RSpec::Mocks::MessageExpectation:0x00000002bd6e18>
     # ./lib/simple_navigation/adapters/sinatra.rb:14:in `initialize'
     # ./spec/lib/simple_navigation/adapters/padrino_spec.rb:6:in `new'
     # ./spec/lib/simple_navigation/adapters/padrino_spec.rb:6:in `create_adapter'
     # ./spec/lib/simple_navigation/adapters/padrino_spec.rb:13:in `block (2 levels) in <top (required)>'

  2) SimpleNavigation::Adapters::Padrino content_tag should delegate to context
     Failure/Error: SimpleNavigation::Adapters::Padrino.new(@context)
     NoMethodError:
       undefined method `request' for #<RSpec::Mocks::MessageExpectation:0x00000002bc7468>
     # ./lib/simple_navigation/adapters/sinatra.rb:14:in `initialize'
     # ./spec/lib/simple_navigation/adapters/padrino_spec.rb:6:in `new'
     # ./spec/lib/simple_navigation/adapters/padrino_spec.rb:6:in `create_adapter'
     # ./spec/lib/simple_navigation/adapters/padrino_spec.rb:13:in `block (2 levels) in <top (required)>'

  3) SimpleNavigation::Adapters::Rails self.register should call set_env
     Failure/Error: @context.stub!(:controller => @controller)
     NoMethodError:
       undefined method `stub!' for #<RSpec::Mocks::MessageExpectation:0x00000002b7e740>
     # ./spec/lib/simple_navigation/adapters/rails_spec.rb:12:in `block (2 levels) in <top (required)>'

  4) SimpleNavigation::Adapters::Rails self.register should extend the ActionController::Base with the Helpers
     Failure/Error: @context.stub!(:controller => @controller)
     NoMethodError:
       undefined method `stub!' for #<RSpec::Mocks::MessageExpectation:0x00000002b79ec0>
     # ./spec/lib/simple_navigation/adapters/rails_spec.rb:12:in `block (2 levels) in <top (required)>'

...

422 examples, 356 failures

Full build log:
https://reproducible.debian.net/rb-pkg/unstable/amd64/ruby-simple-navigation.html

-- System Information:
Debian Release: stretch/sid
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 3.19.0-23-generic (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)