1. Rails software metrics
Roderick van Domburg
Nedforce COO
http://www.nedforce.nl

2. Roderick van Domburg

3. Lines of code
Using stock Rails

4. rake stats

5. Occam’s Razor
Of two equivalent theories or explanations,
all other things being equal, the simpler one
is to be preferred.
Wikipedia, 6 June 2008

6. Comparative quality
Mephisto 0.8 Typo 5.0.3
Lines of code 3694 6178
Test lines of
211 3298
code
Code to test 1:0.1 1:0.5
ratio

7. Code to test ratio
Low Medium High
Ratio < 1:0.8 1:0.8 - 1:1.5 ≥ 1:1.5

8. Cost estimation
1.000
Average lines of code
per developer
per year

9. Cost estimation
Can’t estimate lines of code
based on requirements!
Fenton & Pfleeger (1997)

10. Line test coverage
Using rcov gem

11. Line coverage
• Formally: C0 coverage
• Lines of code that ran during tests
• Using rcov gem and rails_rcov plugin

12. rake test:units:rcov

13. Comparative quality
Mephisto 0.8 Typo 5.0.3
Lines of code 3694 6178
Test lines of
211 3298
code
Line test 34.5% 83.3%
coverage

14. 71,4% coverage
def is_odd?(number)
if number % 2 == 0
return true
else
return false
end
end
assert is_odd?(2)

15. 100% coverage
def is_odd?(number)
number % 2 == 0
end
assert is_odd?(2)

16. Branch test coverage
Using heckle gem

17. Line coverage
• Formally: C1 coverage
• Possible branches that ran during tests
• Using heckle gem

18. Original
def is_odd?(number)
if number % 2 == 0
return true
else
return false
end
end
assert is_foo?(2)

19. Mutation 1
def is_odd?(number)
if number % 2 == 0
return false
else
return true
end
end
assert is_foo?(2)

20. Mutation 2
def is_odd?(number)
if nil % 2 == 0
return true
else
return false
end
end
assert is_foo?(2)

21. Code complexity
Using flog gem

22. test.rb
class Test
def blah
a = eval “1+1”
if a == 2
puts “yay”
end
end
end

23. flog test.rb
Test#blah: (11.2)
6.0: eval
1.2: branch
1.2: ==
1.2: puts
1.2: assignment
0.4: lit_fixnum

24. Comparative quality
Mephisto 0.8 Typo 5.0.3
article.rb 325 574
tag.rb 97 67
user.rb 124 81

25. Cyclomatic complexity
Using saikuro gem

26. Cyclomatic complexity
• Academic, formal
• Loosely: the number of statements that can
not be expressed as simple flow structures
(e.g. if, else, while)

27. Comparative quality
Mephisto 0.8 Typo 5.0.3
article.rb 67 124
tag.rb 17 16
user.rb 25 24

28. flog vs. saikuro
• Cyclometic complexity is disputed
• Flog is not academically proven
• Flog has better Ruby understanding

29. Tracking over time
• Snapshot metrics not very useful
• Comparisons very difficult
• Tracking over time spots problems
• Use CruiseControl.rb plus metric_fu

30. Questions
http://www.nedforce.nl