String Calculator TDD Kata Created by Roy Osherove http://osherove.com/tdd-kata-1 Ruby Solution based on performance by Corey Haines http://katas.softwarecraftsmanship.org/?p=80
Wednesday, April 27, 2011
Basic Requirements •
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”
Wednesday, April 27, 2011
Rules •
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
Wednesday, April 27, 2011
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
Wednesday, April 27, 2011
The Empty String
What’s a StringCalculator?
`const_missing': uninitialized constant Object::StringCalculator (NameError) Wednesday, April 27, 2011
The Empty String
That’s nicer.
Wednesday, April 27, 2011
The Empty String
This is what we are looking for.
Wednesday, April 27, 2011
The Empty String
“Remember to solve things as simply as possible”
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Single numbers
Duplication
Wednesday, April 27, 2011
Saw that one coming.
Single numbers
Duplication
Wednesday, April 27, 2011
“Remember to solve things as simply as possible”
Single numbers
What if we could say it like this?
Wednesday, April 27, 2011
Single numbers
Duplication removed. Don’t get distracted by RSpec syntax. Wednesday, April 27, 2011
Single numbers
Expected that, but why don’t I see the actual value returned? Wednesday, April 27, 2011
Single numbers
Still red, but the message is much better. Wednesday, April 27, 2011
Single numbers
Getting smarter.
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Two numbers
How did it come up with 2? Wednesday, April 27, 2011
Two numbers
“Remember to solve things as simply as possible”
Wednesday, April 27, 2011
Two numbers
Two digit number throws a monkey wrench. Wednesday, April 27, 2011
Two numbers Getting a little more general.
How many times can you say ‘to_i’?
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Two numbers Still green.
Now there are a lot of details here.
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Two numbers
Still green and add is a little cleaner now
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New Requirement
Allow the Add method to handle an unknown amount of numbers
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Three numbers
Red
Wednesday, April 27, 2011
Three numbers Why is cheating so much fun?
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Three numbers
Busted.
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Three numbers More general.
Are there really 3 different cases here?
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Three numbers Ah, that’s nicer.
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Many numbers
Passes as-is.
Wednesday, April 27, 2011
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)
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New lines as delimiters
Red.
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New lines as delimiters
Green.
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‘,’ is duplicated.
New lines as delimiters
Hide that literal away in a descriptively named method
Wednesday, April 27, 2011
New lines as delimiters
Passes as-is.
Wednesday, April 27, 2011
New Requirement Support 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
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Custom delimiters
Bonus Points: Why did it return 1?
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Custom delimiters
Hard coding
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Delimiter abstraction comes in handy - we only changed one method.
Custom delimiters
Red
Wednesday, April 27, 2011
Custom delimiters
Are the concepts clear here?
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Replace constant with variable
Custom delimiters
No comments needed.
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Custom delimiters
A little less noise.
Wednesday, April 27, 2011
Custom delimiters
You can memoize the delimiter if you only want to calculate it once.
Wednesday, April 27, 2011
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
Wednesday, April 27, 2011
Negative Numbers
Red.
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Negative Numbers
“Remember to solve things as simply as possible”
Wednesday, April 27, 2011
Negative Numbers
add reads like the requirements
Wednesday, April 27, 2011
Negative Numbers
Red.
Wednesday, April 27, 2011
Negative Numbers
Refactor in the green. Wednesday, April 27, 2011
Negative Numbers
Extract a method
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A little memoization
Negative Numbers
Back to Red.
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Negative Numbers
Done.
Wednesday, April 27, 2011
Checking your answers git diff master
Starting fresh git reset --hard HEAD
Wednesday, April 27, 2011
