copy edits [ci skip]

activerecord/lib/active_record/relation/calculations.rb

@@ -14,7 +14,7 @@ module Calculations
     #   Person.count(:age, distinct: true)
     #   # => counts the number of different age values
     #
-    # If used on a +group+, it returns a Hash whose keys represent the aggregated column,
+    # If +count+ is used with +group+, it returns a Hash whose keys represent the aggregated column,
     # and the values are the respective amounts:
     #
     #   Person.group(:city).count

guides/source/testing.md

@@ -774,10 +774,10 @@ You don't need to set up and run your tests by hand on a test-by-test basis. Rai
 Brief Note About `Test::Unit`
 -----------------------------
 
-Ruby ships with a boat load of libraries. In Ruby 1.8 one little gem of a library is `Test::Unit`, a framework for unit testing in Ruby. All the basic assertions discussed above are actually defined in `Test::Unit::Assertions`. The class `ActiveSupport::TestCase` which we have been using in our unit and functional tests extends `Test::Unit::TestCase`, allowing
+Ruby ships with a boat load of libraries. Ruby 1.8 provides `Test::Unit`, a framework for unit testing in Ruby. All the basic assertions discussed above are actually defined in `Test::Unit::Assertions`. The class `ActiveSupport::TestCase` which we have been using in our unit and functional tests extends `Test::Unit::TestCase`, allowing
 us to use all of the basic assertions in our tests.
 
-Ruby 1.9 introduced MiniTest, an updated version of Test::Unit which provides a backwards compatible API for Test::Unit. You could also used MiniTest in Ruby 1.8 by installing the `minitest` gem.
+Ruby 1.9 introduced `MiniTest`, an updated version of `Test::Unit` which provides a backwards compatible API for `Test::Unit`. You could also use `MiniTest` in Ruby 1.8 by installing the `minitest` gem.
 
 NOTE: For more information on `Test::Unit`, refer to [test/unit Documentation](http://ruby-doc.org/stdlib/libdoc/test/unit/rdoc/)
 For more information on `MiniTest`, refer to [Minitest](http://www.ruby-doc.org/stdlib-1.9.3/libdoc/minitest/unit/rdoc/)