```ruby
class MiniTest::Spec
  
  class << self 

    #
    # Evaluates a context by name.
    #
    # @example  
    #   describe ExampleClass do
    #     inherit_context :example
    #   end
    #
    # @param [Symbol] name
    #   The name of a context defined by {MiniTest::Context.define define}.
    #
    # @raise [ArgumentError]
    #   Raises an ArgumentError if a context by name does not exist.
    #
    # @return [void] 
    #
    def inherit_context name
      if MiniTest::Context.list.has_key?(name) 
        MiniTest::Context.list[name].each do |context| 
          class_eval &context
        end
      else
        raise ArgumentError, "No context with #{name} found."
      end
    end

  end

end
```

Improve the ArgumentError exception message in inherit_context.
user
```ruby
class MiniTest::Spec
  
  class << self 

    #
    # Evaluates a context by name.
    #
    # @example  
    #   describe ExampleClass do
    #     inherit_context :example
    #   end
    #
    # @param [Symbol] name
    #   The name of a context defined by {MiniTest::Context.define define}.
    #
    # @raise [ArgumentError]
    #   Raises an ArgumentError if a context by name does not exist.
    #
    # @return [void] 
    #
    def inherit_context name
      if MiniTest::Context.list.has_key?(name) 
        MiniTest::Context.list[name].each do |context| 
          class_eval &context
        end
      else
        raise ArgumentError, "No context by name '#{name}' found."
      end
    end

  end

end
```
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