Test First Teaching and the path to TDD

Test First Teaching
and the path to TDD

Who am I?

Sarah Allen
@ultrasaurus

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...

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

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

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

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/

How do we know it's a
good idea?

it works

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

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/)

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

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/

Methodology

• Run the test
• Watch it fail
• Write code to ﬁx the ﬁrst failure
• See it pass
• Refactor

Sound familiar?

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

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

TFT Example

Let's look at some code

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
end

it "adds positive numbers" do
end

it "subtracts numbers" do
@calculator.subtract(10,4).should == 6
end
end

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"
end

end

Solutions for
Challenging
Idioms
blocks
time
method missing
builder pattern

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

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

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());
}

ruby koans

• self-guided, test-driven
• Ruby language basics
• very fun, whimsical and elegant

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

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

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).

Design

Focus

Collaboration

Testing

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

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.

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.

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!

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

testfirst.org

http://github.com/ultrasaurus/test-first-teaching

Many thanks to: Alex Chaffee, Liah Hansen and others

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)

Learning should be fun

• Questions?

Test First Teaching and the path to TDD

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