Test First Teaching background and methodology for teaching programming using automated test frameworks, how this relates to (and can lead to learning) test-driven development

1. Test First Teaching
and the path to TDD

2. Who am I?
Sarah Allen
@ultrasaurus

4. Why should you care?
• you want to improve your Ruby skills
• you want to do testing (better)
• you have a friend or colleague who wants to
learn Ruby
• you want to help us improve our materials
• by teaching, you learn...

5. by teaching, you learn...
• the best engineers are good teachers
• we live and work in collaborative
environments
• it is not enough to know any single thing well
• we must teach in order to effectively produce
software

6. What is
Test-First Teaching?
• teacher provides microtests
• student makes them pass
• one test at a time
• can be used guided (in classroom) or solo
• or with a pair

7. Pairing Is Teaching

8. Pairing in the classroom
• students learn together and teach each other
• each pair can proceed through exercises at
their own pace
• teacher is freed to wander the room

9. How do we know it's a
good idea?
2002 Alex Chaffee
jGuru Java curriculum
2005 Mike Clark
many Ruby Learning Tests
independent 2006 ara.t.howard
inventors Ruby Quiz #67
"Metakoans"
2008 Yehuda Katz
& Matt Aimonetti
Ruby on Rails training
and many more...
http://www.flickr.com/photos/annais/9335897/sizes/z/

10. How do we know it's a
good idea?
it works

11. Learning Ruby via Tests
• [Test-First Teaching](http://testfirst.org)
by Sarah Allen and Alex Chaffee
• [Ruby Koans](http://rubykoans.com)
by Jim Weirich and Joe O’Brien
• [Metakoans](http://rubyquiz.com/quiz67.html)
by ara.t.howard

12. Other Guided Learning
• [ruby-warrior](http://github.com/ryanb/ruby-warrior) by Ryan
Bates - a game written in Ruby for learning Ruby
• [Try Ruby](http://tryruby.org) runs a Ruby interpreter in your
browser, with hints and advice
• [Growing OO Software In Ruby](http://www.exampler.com/
blog/2009/12/17/growing-object-oriented-software-in-ruby/) by
Brian Marick
• Ruby version of [Growing Object-Oriented Software
Guided by Tests](http://www.growing-object-oriented-
software.com/)

13. Created by:
Sarah Allen
Alex Chaffee
Liah Hansen
and friends
Test-First Teaching....
http://testfirst.org
Maybe we should call it Test-First Learning
http://github.com/ultrasaurus/test-first-teaching

14. Traditional Professional
Programming Classes
Big, Boring Lecture
Followed by Exercises
• multiple choice
• fill in the blanks with words
or pseudocode
• skeleton code - big program
with chunks excised and
replaced with comments
• large task - soup to nuts
without feedback
.flickr.com/photos/chasephotography/3890300709/

15. writing code
is engaging

16. Methodology
• Run the test
• Watch it fail
• Write code to fix the first failure
• See it pass
• Refactor
Sound familiar?

17. Why TFT?
• makes the assignment very clear
• student gets immediate feedback on progress
(or lack thereof)
• removes the magic
• leads the student through all the steps to
writing the code
• teaches student to read errors

18. Embrace Failure

19. Embrace Failure
• start from a point of failure
• it feels like it's not your fault
• people learn better when they're not stressed
• playfulness enhances learning

20. TFT Example
Let's look at some code

21. Objects and Methods
require "calculator"
describe Calculator do
before do
@calculator = Calculator.new
end
it "adds 0 and 0" do
@calculator.add(0,0).should == 0
end
it "adds 2 and 2" do
@calculator.add(2,2).should == 4
end
it "adds positive numbers" do
@calculator.add(2,6).should == 8
end
it "subtracts numbers" do
@calculator.subtract(10,4).should == 6
end
end

23. TDD Extra Credit!
# Test-Driving Bonus: once the above tests pass,
# write tests and code for the following:
it "multiplies two numbers"
it "multiplies an array of numbers"
it "raises one number to the power of another number"
# http://en.wikipedia.org/wiki/Factorial
describe "#factorial" do
it "computes the factorial of 0"
it "computes the factorial of 1"
it "computes the factorial of 2"
it "computes the factorial of 5"
it "computes the factorial of 10"
end
end

24. But...
that's
impossible

25. Solutions for
Challenging
Idioms
blocks
time
method missing
builder pattern

26. Blocks
require "performance_monitor"
(and mocks) it "takes exactly 1 second to run a block that
describe PerformanceMonitor do sleeps for 1 second (with stubs)" do
before do fake_time = 100
@monitor = PerformanceMonitor.new Time.stub!(:now).and_return {fake_time}
end @monitor.run do
fake_time += 1
it "takes about 0 seconds to run an empty block" do end.should == 1
@monitor.run do end
end.should be_close(0, 0.1)
end it "runs a block N times" do
n = 0
it "takes exactly 0 seconds to run an empty block @monitor.run(4) do
(with stubs)" do n += 1
Time.stub!(:now).and_return(100) end
@monitor.run do n.should == 4
end.should == 0 end
end
it "returns the average time, not the total time,
it "takes about 1 second to run a block that sleeps when running multiple times" do
for 1 second" do run_times = [8,6,5,7]
@monitor.run do run_index = 0
sleep 1 fake_time = 100
end.should be_close(1, 0.1) Time.stub(:now).and_return { fake_time }
end @monitor.run(4) do
fake_time += run_times[run_index]
run_index += 1
end.should == 6
end
end

27. method_missing, nested
closures, and the builder pattern
require "xml_document"
it "nests several levels" do
describe XmlDocument do @xml.hello do
before do @xml.goodbye do
@xml = XmlDocument.new @xml.come_back do
end @xml.ok_fine(:be => "that_way")
end
it "renders an empty tag" do end
@xml.hello.should == "<hello/>" end.should ==
end "<hello><goodbye><come_back><ok_fine be='that_way'/
></come_back></goodbye></hello>"
it "renders a tag with attributes" do end
@xml.hello(:name => 'dolly').should == "<hello
name='dolly'/>" it "indents" do
end @xml = XmlDocument.new(true)
@xml.hello do
it "renders a randomly named tag" do @xml.goodbye do
tag_name = (1..8).map{|i| @xml.come_back do
('a'..'z').to_a[rand(26)]}.join @xml.ok_fine(:be => "that_way")
@xml.send(tag_name).should == "<#{tag_name}/>" end
end end
end.should ==
it "renders block with text inside" do "<hello>n" +
@xml.hello do " <goodbye>n" +
"dolly" " <come_back>n" +
end.should == "<hello>dolly</hello>" " <ok_fine be='that_way'/>n" +
end " </come_back>n" +
" </goodbye>n" +
it "nests one level" do "</hello>n"
@xml.hello do end
@xml.goodbye end
end.should == "<hello><goodbye/></hello>"
end

28. threads
(sorry for the Java)
public void testThreadSafe() throws InterruptedException
{
int DEPOSITORS = 50;
int AMOUNT = 2;
// note: increase this value until it *fails* on your CPU.
// Then fix it.
int REPS = 25000;
Account account = new Account("Joe", 0);
Thread[] depositors = new Thread[DEPOSITORS];
for (int i=0; i< DEPOSITORS; ++i) {
depositors[i] = new Depositor(account, AMOUNT, REPS);
depositors[i].start();
}
for (int i=0; i< DEPOSITORS; ++i) {
depositors[i].join();
}
assertEquals(REPS * DEPOSITORS * AMOUNT, account.getBalance());
}

29. ruby koans
• self-guided, test-driven
• Ruby language basics
• very fun, whimsical and elegant

30. ruby koans example
require File.expand_path(File.dirname(__FILE__) + '/edgecase')
class AboutStrings < EdgeCase::Koan
def test_double_quoted_strings_are_strings
string = "Hello, World"
usually self-
assert_equal __, string.is_a?(String)
end contained
def test_single_quoted_strings_are_also_strings
just tests and fixtures,
string = 'Goodbye, World' with no class declaration
assert_equal __, string.is_a?(String)
end
def test_use_single_quotes_to_create_string_with_double_quotes
“fill in the
string = 'He said, "Go Away."'
assert_equal __, string blanks”
end
technique
def test_use_double_quotes_to_create_strings_with_single_quotes
string = "Don't"
assert_equal __, string
end
teaching through
def test_use_backslash_for_those_hard_cases practice and
a = "He said, "Don't""
b = 'He said, "Don't"' challenge
assert_equal __, a == b
end

31. TFT != TDD
• Mechanics of testing are hard to learn
• TFT teaches programming; TDD is design
• At the end of some modules,
students write their own tests for “extra
credit”
• doesn’t really flex the creative muscles
required for software design

32. What about TDD?
• easier to learn TDD, post-TFT
• know the language
• know the test framework
• used to the rhythm of test-first
• study design patterns, or check out [GOOS]
(http://www.exampler.com/blog/2009/12/17/
growing-object-oriented-software-in-ruby).

33. Testing

34. NOT

35. Test Driven Development

36. Design
Focus
Collaboration
Testing

37. TDD is Design
• You must understand the problem
• The test specifies the interface to the code
– Having a well‐designed interface is o<en more
important than having an efficient implementa>on
• Encourages modular design with clear
dependencies

38. TDD helps you Focus
• Separa>on of Development Phases
– Requirements
– Design
– Implementa>on
• Write all the code you need,
and none of the code you don’t need.

39. TDD enhances Collabora>on
• Encourages breakdown of complexity
• You know when you are done
• Creates a natural check‐in point:
– commit when your tests pass
• Quicker team checkpoints.

40. TDD helps you Test
• High quality tests
– Verifica>on of failure condi>ons (red, green)
– Avoid false posi>ves
• At the end of the project, you have tests!

41. Alex Chaffee

42. Wolfram Arnold

43. How to start TDD?
• Build tests before refactoring or upgrading
• Test‐drive bug fixes
• Write tests for anything you worry about
• Con>nuous Integra>on is essen>al
• Remove unused (untested) code

44. Design
Focus
Collaboration
Testing

45. More Fun!

46. testfirst.org
http://github.com/ultrasaurus/test-first-teaching
Many thanks to: Alex Chaffee, Liah Hansen and others

47. Credits
• Fail Whale illustrated by Yiying Lu (http://
www.yiyinglu.com/)
• Pair Programming photos by Lee Lundrigan
and Sarah Allen
• Thank you Flickr and Creative Commons
(see slides for attribution)

48. Learning should be fun
• Questions?