minitest_assert.rb

require "rubocop"

module RuboCop
  module Cop
    module Lint
      # This cop checks bad use of the Minitest `assert` method
      #
      # `assert` method's second argument is the error message when the
      # first argument evals to false.
      #
      # A common mistake, is to use `assert` instead of `assert_equal`,
      # in that case `assert` will never fail, because the first argument
      # will always be evaluated to true.
      #
      # @example
      #
      #   # bad
      #   assert "foobar", @user.title
      #
      #   # bad
      #   expected = "foobar"
      #   assert expected, @user.title
      #
      #   # good
      #   assert_equal "foobar", @user.title
      #   assert user.title?, "User should have a title"
      #
      class MinitestAssert < Cop
        MSG = "Use assert_equal to compare two values and not assert. The second argument on assert is the message."

        def initialize(*)
          super
          @local_literal = Set.new
        end

        def on_send(node)
          receiver, method_name, *args = *node

          if receiver == nil && method_name == :assert && args[1]
            if args.first.truthy_literal? && :true != args.first.type
              add_offense(node, :selector)
            elsif args.first.variable? && @local_literal.include?(args.first.children.first)
              add_offense(node, :selector)
            end
          end
        end

        def on_def(_node)
          @local_literal = Set.new
        end
        alias on_defs on_def

        def on_lvasgn(node)
          left, right = *node
          return unless right
          if right.literal? && :true != right.type && :false != right.type
            @local_literal << left
          else
            @local_literal.delete(left)
          end
        end

      end
    end
  end
end