A TDD tutorial on implementing Dijkstra's shortest path algorithm in PHP with test-driven development and PHPUnit.

1. Got units?
Bengaluru, 20-22 November 2011

2. TDD
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3. RED
add a test, it won't pass
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4. GREEN
implement the necessary code to make the test pass
Bengaluru, 20-22 November 2011

5. REFACTOR
polish the code
Bengaluru, 20-22 November 2011

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

7. Bengaluru, 20-22 November 2011

8. Bengaluru, 20-22 November 2011

9. Bengaluru, 20-22 November 2011

10. Bengaluru, 20-22 November 2011

11. Bengaluru, 20-22 November 2011

12. Bengaluru, 20-22 November 2011

13. Bengaluru, 20-22 November 2011

14. Bengaluru, 20-22 November 2011

15. Bengaluru, 20-22 November 2011

16. github.com/odino/osidays
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17. git checkout $step
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18. Step 0/1
● create the directory structure
● add Symfony2 classloader as submodule
● init and update submodule
● (optional) create an empty class
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19. Step 2
● write the test with the smallest
amount of code you think it's
necessary
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20. Step 3
● add the Vertex class
● add the Graph class
● add an empty solve() method
for the algorithm class
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21. Step 4
● implement the solve method
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22. Step 5
● added all the methods
needed by the Dijkstra::solve()
● need to implement Graph::calculatePotentials()
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23. Step 6
● a test is added for the Graph class
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24. Step 7
● calculatePotentials() is tested
● half of our test-suite passes
● switch back to the Dijkstra's test
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25. Step 8
● minor tweaks to make all the tests pass
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26. 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
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27. Step 10
● since we like to be OO, we can connect
vertices through objects, and not
arrays anymore
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28. Step 11
● we now need to fix the code which
uses vertices' connections as arrays
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29. Step 12
● the library seems pretty complete
● PHPDoc is added
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30. 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
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31. Step 14
● implementation
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32. Step 15
● enter Mocking objects
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33. Step 16
● Dijkstra::getGraph() seems to be useless
so we probably don't need any Graph class
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34. Step 17
● removed Graph class
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35. Step 18
● some tests rely on it, so we need to
eliminate old references to Graph
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36. Step 19
● enter Data Providers
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37. Step 20
● what about calculating the path between
not-connected vertices?
It should return null, so code is refactored
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38. 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
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39. Alessandro Nadalin
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40. odino.org
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41. Bengaluru, 20-22 November 2011

42. @_odino_ #osidays
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43. REST in peace: tomorrow, 12.45
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44. Thank YOU!
@_odino_
Bengaluru, 20-22 November 2011