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Wrong provides a general assert method that takes a predicate block. Assertion failure messages are rich in detail. The Wrong idea is to replace all those countless assert\_this, assert\_that, should\_something library methods which only exist to give a more useful failure message than "assertion failed". Wrong replaces all of them in one fell swoop, since if you can write it in Ruby, Wrong can make a sensible failure message out of it.

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  1. 1. http://xkcd.com/386/ Wrong The right way to assert
  2. 2. Time Is Money (Test::Unit) assert_equal money, time • verb is moved to front • direct and indirect objects (expected and actual) are reversed
  3. 3. Time Is Money (RSpec) time.should ==(money) • confusing syntax -- space vs. dot vs. underscore vs. parens • == looks familiar, but “should” is inserted between parameters so it’s not apparent what the calculation is
  4. 4. Time Is Money (Minitest) assert time == money • Ah, now I see what you mean • Default failure message is not helpful “Failed assertion, no message given.” • Making the message helpful violates DRY assert time == money, “Time should equal money”
  5. 5. Time Is Money (Wrong) assert { time == money } • Failure message is helpful: Expected (time == money), but 6 is not equal to 27 time is 6 money is 27
  6. 6. How do we do it?
  7. 7. Magic • RubyParser and Ruby2Ruby by Ryan Davis • We turn the block into source code, parse it into an AST, break it down into parts, then convert back to code for the messages
  8. 8. Also, we cheat • We open the source file on disk, jump to the right line, and parse it • If you’re constructing your tests with metaprogramming, you’ve got bigger problems than not being able to use Wrong
  9. 9. Less Is More Test::Unit Asserts RSpec Matchers assert_block { x } x.should be_true assert(x) x.should be_false assert_equal x, y assert_raise LoadError { x } x.should be_nil assert_raise { x } x.should == y assert_raise LoadError.new("why") { x } x.should >= y assert { ... } assert_raise(RuntimeError, LoadError) { x } x.should be_something(y) assert_raise_kind_of(LoadError) { x } assert_instance_of(String, x) x.should be_close(y, delta) assert_instance_of([String, Fixnum], x) x.should be_instance_of y assert_nil x x.should be_an_instance_of y assert_kind_of x.should be_kind_of y assert_respond_to x, :to_y assert_match /regex/, s x.should be_a_kind_of y" assert_same x, y x.should eql(y) deny { ... } assert_operator x, :>=, y x.should equal(y) assert_nothing_raised x x.should exist flunk assert_not_same x,y team.should have(11).players assert_not_equal x,y [1,2,3].should have(3).items assert_not_nil "this string".should have(11).characters assert_no_match regex, x x.should have_at_least(number).items assert_throw assert_throws x.should have_at_most(number).items assert_nothing_thrown x.should include(y) assert_in_delta f, g, delta x.should match(/regex/) assert_send [o, m, arg1, arg2] lambda { do_something_risky }.should raise_exception assert_boolean x assert_true x lambda { do_something_risky }.should raise_exception assert_false x (PoorRiskDecisionError) assert_compare x, ">=", y lambda { do_something_risky }.should raise_exception assert_fail_assertion { x } (PoorRiskDecisionError) { |exception| assert_raise_message m, { x } assert_const_defined Test, :Unit exception.data.should == 42 } assert_not_const_defined Test, :Unit lambda { do_something_risky }.should raise_exception assert_predicate o, :empty? (PoorRiskDecisionError, ""that was too risky"") assert_not_predicate lambda { do_something_risky }.should raise_exception assert_alias_method assert_path_exist "/foo" (PoorRiskDecisionError, /oo ri/) assert_path_not_exist "/foo" x.should respond_to(*names)
  10. 10. Helpers • rescuing { } • capturing { } • close_to? • assert { x.close_to?(y) } • assert { x.close_to?(y, delta) }
  11. 11. Frameworks • Minitest • RSpec • Test::Unit • ???
  12. 12. Explanations assert("since we're on Earth") { sky.blue? }
  13. 13. Color • Because you can’t succeed without it
  14. 14. Info • Authors • Steve Conover - <sconover@gmail.com> • Alex Chaffee - <alex@stinky.com> - <http://alexch.github.com> • Github: <http://github.com/alexch/wrong> • Tracker: <http://www.pivotaltracker.com/ projects/109993>