ruby-rspec-rails: FTBFS: cannot load such file -- rspec/core/deprecation (LoadError)

[Logan Rosen]

Imported from Debian bug http://bugs.debian.org/799821:

Source: ruby-rspec-rails
Version: 2.14.2-1
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:

┌──────────────────────────────────────────────────────────────────────────────┐
│ Run tests for ruby2.1 from debian/ruby-tests.rake │
└──────────────────────────────────────────────────────────────────────────────┘

RUBYLIB=/ruby-rspec-rails-2.14.2/debian/ruby-rspec-rails/usr/lib/ruby/vendor_ruby:. rake2.1 -f debian/ruby-tests.rake
/usr/bin/ruby2.1 /usr/bin/rspec --pattern ./spec/rspec/\*\*/\*_spec.rb
/usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- rspec/core/deprecation (LoadError)
 from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
 from /usr/lib/ruby/vendor_ruby/active_support/dependencies.rb:247:in `block in require'
 from /usr/lib/ruby/vendor_ruby/active_support/dependencies.rb:232:in `load_dependency'
 from /usr/lib/ruby/vendor_ruby/active_support/dependencies.rb:247:in `require'
 from /ruby-rspec-rails-2.14.2/lib/rspec/rails/matchers.rb:1:in `<top (required)>'
 from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
 from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
 from /usr/lib/ruby/vendor_ruby/active_support/dependencies.rb:247:in `block in require'
 from /usr/lib/ruby/vendor_ruby/active_support/dependencies.rb:232:in `load_dependency'
 from /usr/lib/ruby/vendor_ruby/active_support/dependencies.rb:247:in `require'
 from /ruby-rspec-rails-2.14.2/lib/rspec/rails.rb:12:in `<top (required)>'
 from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
 from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
 from /ruby-rspec-rails-2.14.2/spec/spec_helper.rb:9:in `<top (required)>'
 from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
 from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
 from /ruby-rspec-rails-2.14.2/spec/rspec/rails/assertion_adapter_spec.rb:1:in `<top (required)>'
 from /usr/lib/ruby/vendor_ruby/rspec/core/configuration.rb:1327:in `load'
 from /usr/lib/ruby/vendor_ruby/rspec/core/configuration.rb:1327:in `block in load_spec_files'
 from /usr/lib/ruby/vendor_ruby/rspec/core/configuration.rb:1325:in `each'
 from /usr/lib/ruby/vendor_ruby/rspec/core/configuration.rb:1325:in `load_spec_files'
 from /usr/lib/ruby/vendor_ruby/rspec/core/runner.rb:103:in `setup'
 from /usr/lib/ruby/vendor_ruby/rspec/core/runner.rb:89:in `run'
 from /usr/lib/ruby/vendor_ruby/rspec/core/runner.rb:74:in `run'
 from /usr/lib/ruby/vendor_ruby/rspec/core/runner.rb:42:in `invoke'
 from /usr/bin/rspec:4:in `<main>'
/usr/bin/ruby2.1 /usr/bin/rspec --pattern ./spec/rspec/\*\*/\*_spec.rb failed
ERROR: Test "ruby2.1" failed. Exiting.
dh_auto_install: dh_ruby --install /ruby-rspec-rails-2.14.2/debian/ruby-rspec-rails returned exit code 1

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

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