parser_for_testing.rb

require 'ripper'

class TestParser < Ripper::SexpBuilder
  def self.from_file(filename)
    TestParser.new(File.read(filename))
  end

  def parse
    @methods = []
    @calls   = []
    super
  end

  def on_def(*args)
    # [:def, [:@ident, "db", [35, 8]], [:params, nil, nil, nil, nil, nil], [:bodystmt, [:stmts_add, [:stmts_new], [:var_ref, [:@ivar, "@con", [36, 6]]]], nil, nil, nil]]
    super.tap do |(_def, (_ident, name, _coords), *other)|
      @methods << name
    end
  end

  def on_call(*args)
    # [[:call, [:var_ref, [:@ident, "db", [66, 10]]], :".", [:@ident, "rename_job!", [66, 13]]]]
    super.tap do |(_call, (_var_ref, (_ident, name, _coords)), _dot, (_ident2, method_name, (line, column)))|
      if String === name && String === method_name
        @calls << [ name, method_name, line, column ]
      end
    end
  end

  def methods
    @methods ? @methods : parse && @methods
  end

  def calls
    @calls ? @calls : parse && @calls
  end

  def defines_method?(m)
    methods.include?(m)
  end

  def method_calls_on(ident)
    calls.select { |(an_ident, method_name, line)| an_ident == ident }
  end
end

usage.rb

# filter a list of files based on methods they define somewhere:
filenames.select do |filename|
  TestParser.from_file(filename).defines_method?('foo')
end

# compare method calls to a list of methods and make the test fail if there is a call to a non-existing method:
defined_methods = my_object.public_methods(true).map(&:to_s)
TestParser.from_file(filename).
  method_calls_on('a_name_i_always_use_for_that_kind_of_object').select do |_, method_name, _, _|
    !defined_methods.include?(method_name)
  end.should == []