Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Questions.
• BDD Basics.
• Cucumber Basics.
• Some Examples.
• Homework time.

Preliminaries

Admin

• We are continuing to hit transition problems. I'll do my best to help you work through them.
• Mr. Stone will be teaching next week's class.

Homework

• No matter what it says online, your homework is at https://github.com/saasbook/hw-bdd-cucumber. (Agh! I gave you the wrong one for this week. Fortunately, none of you started.)
• You will also be doing some readings on computer ethics for next class. Expect an email about that tonight (although I think I've gotten it into the site for now).

Questions

• The only programming homework is hw-bdd-cucumber
• The only reading is the ethics readings
• Yes, you still have to journal.

Behavior-Driven Development

• What do you see as the key features of BDD?
• What are the relationships you see between BDD and TDD? Similarities and differences?
• Some folks have suggested that we replace TDD with BDD. Does that seem like a good idea? Why or why not?

Key Features of BDD

• A programmatic mechanism for checking whether programs do what people want them to do.
• We think about what the program does in terms of overall behavior. ("Big picture")
• Typically written in a style that is understandable to non-technical people. Potentially easier to understand.
• At least in cucumber, we think about things hierarchically
  • We break overall utility into features
  • We break features into scenarios
  • We break scenarios into steps or declarations
• In most BDD systems, we focus on user stories

Similarities between BDD and TDD

• Both automated ways to check "if things are working right"
• Both expect you to express criteria for your tests
• Both expect you to write criteria in advance of writing code
• Both are video games. Turn everything green!

Differences between BDD and TDD

• Difference audience: TDD tests don't have to be written for non-technical people.
• BDD is often big picture, TDD is often smaller pieces.
• BDD is a bit easier to tell when you're done. "Look, the user is happy!"
• TDD encourages us to focus more on edge cases, whereas BDD is more about general cases (although it does include some edge-like cases)
• BDD and TDD give different kinds of confirmation

Should we replace TDD with BDD? (or vice versa)

    As a programmer
    I want the sqrt function to behave appropriately
    so that I can write valid code

    For example,

      When I give 4 an input to sqrt
      Then I expect to get 2 as an output
      When I give -4 as an input to sqrt
      Then I expect to get 0+2i as an output
      Wehn I give "frog" as an input to sqrt
      Then I expect to get an error message

    check_equal(2, sqrt(4));
    check_equal(imaginary(0,2), sqrt(-4));

Arguments for:

• You can show your client (or your manager) something that he/she/ze can understand.
• Learning one system well is easier than learning two systems well.

Arguments against:

• We're programmers, we don't need such verbose "code"
  • BDD seems to have much more running time overhead
• Different intent, so use different systems; use things how they are designed. "If all you have is BDD, everything is a behavior."
  • TDD system features are likely to be different than BDD features; use the things that have the right features.
• Don't abuse tools (don't hack things to make them work for something else)
  • BDD shouldn't be technical testing
• Separate domains!
  
  • Two ways to think about the example above: Programmer and Client

Cucumber

• As we think about behaviors, will we need to work on the model, the view, or the controller?
• What changes are we likely to have to make?
• What step definitions will we have to write to get the text to call Ruby/Rails code?

Feature: search for movies by director

  As a movie buff
  So that I can find movies with my favorite director
  I want to include and search on director information in movies I enter

Background: movies in database

  Given the following movies exist:
  | title        | rating | director     | release_date |
  | Star Wars    | PG     | George Lucas |   1977-05-25 |
  | Blade Runner | PG     | Ridley Scott |   1982-06-25 |
  | Alien        | R      |              |   1979-05-25 |
  | THX-1138     | R      | George Lucas |   1971-03-11 |

• Model, View, and/or Controller?
  • Model
  • View (implicit)
• What changes to M, V, C?
  • Model: Add a new field, Director using the wonders of Migration
  • View (implicit): You need to be able to see the new field in the listing of movies.
• Step definition? movies.each do |movie| addMovie movie.title, movie.rating, ... end

Scenario: add director to existing movie
  When I go to the edit page for "Alien"
  And  I fill in "Director" with "Ridley Scott"
  And  I press "Update Movie Info"
  Then the director of "Alien" should be "Ridley Scott"

• Model, View, or Controller (plus changes)
  • View: The edit page needs a text field named "Director".
  • View: The "Update Movie Info" button might need to be changed. (maybe not, depending on how we phrase the query it makes)
  • Controller: The update method may need to be changed to include the director.
  • Model: We changed it above.
• Step definition?
  • /^I go to the edit page for "([^"])"$/, should be built into Capabyra.
  • /^I fill in "([^"])" with "([^"])"$/, shuld be built into Capabyra.
  • /^I press "([^"])"$/, should be built into Capabyra
  • Then the director of "Alien" should be "Ridley Scott"
    • Simple database query

Scenario: find movie with same director
  Given I am on the details page for "Star Wars"
  When  I follow "Find Movies With Same Director"
  Then  I should be on the Similar Movies page for "Star Wars"
  And   I should see "THX-1138"
  But   I should not see "Blade Runner"

Scenario: can't find similar movies if we don't know director (sad path)
  Given I am on the details page for "Alien"
  Then  I should not see "Ridley Scott"
  When  I follow "Find Movies With Same Director"
  Then  I should be on the home page
  And   I should see "'Alien' has no director info"

Work Time