In Rails 5, the schema layer was updated so that indexes could be
created on expressions rather that simply columns. Update
`have_db_index` so that you can test for this.
More reading: <edc2b77187>
* Bring the file up to date style-wise with other matcher files
* Bring the tests up to date with other tests
* Improve error messaging
* Simplify documentation
When running unit tests we need to ensure that we are simulating how
other people will use the matchers as best we can. This means, for
instance, tagging any example groups that test controller matchers as
controller example groups.
* Change 'spec' Rake task to 'spec:unit'
* Require unit_spec_helper.rb in unit tests, not spec_helper.rb
* Re-namespace files in spec/support/unit under UnitTests
* Files in spec/support/unit/helpers no longer automatically add
themselves to RSpec - this happens in unit_spec_helper.rb
* Extract RecordWithDifferentErrorAttributeBuilder and
RecordValidatingConfirmationBuilder to separate files
* Move spec/shoulda to spec/unit_tests/shoulda
* Move spec/support/*.rb to spec/support/unit_tests/{helpers,matchers}
* Move spec_helper.rb to unit_spec_helper.rb
Elliot Winkler