string calculator tdd kata - github•create a simple string calculator with a method add(numbers)...

String Calculator TDD Kata

Created by Roy Osherovehttp://osherove.com/tdd-kata-1

Ruby Solution based on performance by Corey Haineshttp://katas.softwarecraftsmanship.org/?p=80

Wednesday, April 27, 2011

http://osherove.com/

http://osherove.com/

http://osherove.com/tdd-kata-1

http://osherove.com/tdd-kata-1

http://katas.softwarecraftsmanship.org/?p=80

http://katas.softwarecraftsmanship.org/?p=80

• Create a simple string calculator with a method Add(numbers) that takes a string

• The method can take 0, 1 or 2 numbers, and will return their sum (for an empty string it will return 0) for example “” or “1” or “1,2”

Basic Requirements


• Start with the simplest test case of an empty string and move to one and two numbers

• Remember to solve things as simply as possible so that you force yourself to write tests you did not think about

• Remember to refactor after each passing test

Rules


Getting Start from project shell on Github

git clone [email protected]:calebphillips/string_calculator.git

cd string_calculator

gem install bundler

bundle install

git checkout shell

autotest


mailto:[email protected]

mailto:[email protected]

`const_missing': uninitialized constant Object::StringCalculator (NameError)

The Empty String

What’s a StringCalculator?


The Empty String

That’s nicer.


The Empty String

This is what we are looking for.


The Empty String

“Remember to solve things as simply as

possible”


Single numbers

Saw that one coming.

Duplication


Single numbers

Duplication “Remember to solve things as simply as

possible”


Single numbers

What if we could say it like this?


Single numbers

Duplication removed. Don’t get distracted by RSpec

syntax.


Single numbers

Expected that, but why don’t I see the

actual value returned?


Single numbers

Still red, but the message is much

better.


Single numbers

Getting smarter.


Two numbers

How did it come up with 2?


Two numbers


possible”


Two numbers

Two digit number throws a monkey

wrench.


Two numbersGetting a little more general.

How many times can you say ‘to_i’?


Two numbersStill green.

Now there are a lot of details here.


Two numbers

Still green and add is a little cleaner now


New Requirement

Allow the Add method to handle an unknown amount of numbers


Three numbers

Red


Three numbersWhy is cheating

so much fun?


Three numbers

Busted.


Three numbersMore general.

Are there really 3 different cases

here?


Three numbersAh, that’s

nicer.


Many numbers

Passes as-is.


New Requirement

Allow the Add method to handle new lines between numbers (instead of commas).

the following input is ok: “1\n2,3” (will equal 6)the following input is NOT ok: “1,\n” (not need to

prove it - just clarifying)


New lines as delimiters

Red.



Green. ‘,’ is duplicated.



Hide that literal away in a descriptively named

method



Passes as-is.


New RequirementSupport different delimiters

To change a delimiter, the beginning of the string will contain a separate line that looks like this:

“//[delimiter]\n[numbers…]” for example “//;\n1;2” should return three where

the default delimiter is ‘;’ .

The first line is optional - all existing scenarios should still be supported


Custom delimiters

Bonus Points: Why did it return 1?


Custom delimiters

Delimiter abstraction comes in handy - we only

changed one method.

Hard coding


Custom delimiters

Red


Custom delimiters

Replace constant with variable

Are the concepts clear

here?


Custom delimiters

No comments needed.


Custom delimiters

A little less noise.


Custom delimiters

You can memoize the delimiter if you only

want to calculate it once.


New Requirement

Calling Add with a negative number will throw an exception “negatives not allowed” - and the negative

that was passed

If there are multiple negatives, show all of them in the exception message


Negative Numbers

Red.


Negative Numbers


possible”


Negative Numbers

add reads like the requirements


Negative Numbers

Red.


Negative Numbers

Refactor in the green.


Negative Numbers

Extract a method A little

memoization


Negative Numbers

Back to Red.


Negative Numbers

Done.


Checking your answersgit diff master

Starting fresh

git reset --hard HEAD


string calculator tdd kata - github•create a simple string calculator with a method add(numbers)...

Documents