Got units?
Bengaluru, 20-22 November 2011

TDD
Bengaluru, 20-22 November 2011

RED
add a test, it won't pass
Bengaluru, 20-22 November 2011

GREEN
implement the necessary code to make the test pass
Bengaluru, 20-22 November 2011

REFACTOR
polish the code
Bengaluru, 20-22 November 2011

TDD-ing Dijkstra's
shortest path algorithm
in PHP
Bengaluru, 20-22 November 2011

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Bengaluru, 20-22 November 2011

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github.com/odino/osidays
Bengaluru, 20-22 November 2011

git checkout $step
Bengaluru, 20-22 November 2011

Step 0/1
● create the directory structure
● add Symfony2 classloader as submodule
● init and update submodule
● (optional) create an empty class
Bengaluru, 20-22 November 2011

Step 2
● write the test with the smallest
amount of code you think it's
necessary
Bengaluru, 20-22 November 2011

Step 3
● add the Vertex class
● add the Graph class
● add an empty solve() method
for the algorithm class
Bengaluru, 20-22 November 2011

Step 4
● implement the solve method
Bengaluru, 20-22 November 2011

Step 5
● added all the methods
needed by the Dijkstra::solve()
● need to implement Graph::calculatePotentials()
Bengaluru, 20-22 November 2011

Step 6
● a test is added for the Graph class
Bengaluru, 20-22 November 2011

Step 7
● calculatePotentials() is tested
● half of our test-suite passes
● switch back to the Dijkstra's test
Bengaluru, 20-22 November 2011

Step 8
● minor tweaks to make all the tests pass
Bengaluru, 20-22 November 2011

Step 9
● potentials are assigned in the Graph class
but they should belong to the algorithm,
what about refactoring the code?
● since we move the only tested method of Graph
into Dijkstra's class, we can delete the GraphTest
Bengaluru, 20-22 November 2011

Step 10
● since we like to be OO, we can connect
vertices through objects, and not
arrays anymore
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Step 11
● we now need to fix the code which
uses vertices' connections as arrays
Bengaluru, 20-22 November 2011

Step 12
● the library seems pretty complete
● PHPDoc is added
Bengaluru, 20-22 November 2011

Step 13
● Oooops, we forgot to test a scenario:
in Dijkstra's algorithm we need vertices
connected by positive distance
● a test is added, verifying an exception
is raised through annotations
Bengaluru, 20-22 November 2011

Step 14
● implementation
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Step 15
● enter Mocking objects
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Step 16
● Dijkstra::getGraph() seems to be useless
so we probably don't need any Graph class
Bengaluru, 20-22 November 2011

Step 17
● removed Graph class
Bengaluru, 20-22 November 2011

Step 18
● some tests rely on it, so we need to
eliminate old references to Graph
Bengaluru, 20-22 November 2011

Step 19
● enter Data Providers
Bengaluru, 20-22 November 2011

Step 20
● what about calculating the path between
not-connected vertices?
It should return null, so code is refactored
Bengaluru, 20-22 November 2011

Step 21
● Dijkstra::solve() seems to do too
much things, so we split the method
● first demand potentials' calculation
● second demand path finding
● third demand raising the negative-potentials'
exception
● enter phploc
● enter code-coverage
Bengaluru, 20-22 November 2011

Alessandro Nadalin
Bengaluru, 20-22 November 2011

odino.org
Bengaluru, 20-22 November 2011

Bengaluru, 20-22 November 2011

@_odino_ #osidays
Bengaluru, 20-22 November 2011

REST in peace: tomorrow, 12.45
Bengaluru, 20-22 November 2011

Thank YOU!
@_odino_
Bengaluru, 20-22 November 2011