Rails software metricsRoderick van Domburg

Nedforce COO

http://www.nedforce.nl

Roderick van Domburg

Lines of codeUsing stock Rails

rake stats

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

Comparative quality

Mephisto 0.8 Typo 5.0.3

Lines of code

Test lines of code

Code to test ratio

3694 6178

211 3298

1:0.1 1:0.5

Code to test ratio

Low Medium High

Ratio < 1:0.8 1:0.8 - 1:1.5 ≥ 1:1.5

1.000Average lines of code

per developerper year

Cost estimation

Can’t estimate lines of codebased on requirements!

Fenton & Pfleeger (1997)

Cost estimation

Line test coverageUsing rcov gem

Line coverage

• Formally: C0 coverage

• Lines of code that ran during tests

• Using rcov gem and rails_rcov plugin

rake test:units:rcov

Comparative quality

Mephisto 0.8 Typo 5.0.3

Lines of code

Test lines of code

Line test coverage

3694 6178

211 3298

34.5% 83.3%

71,4% coverage

def is_odd?(number) if number % 2 == 0 return true else return false endend

assert is_odd?(2)

100% coverage

def is_odd?(number) number % 2 == 0end

assert is_odd?(2)

Branch test coverageUsing heckle gem

Line coverage

• Formally: C1 coverage

• Possible branches that ran during tests

• Using heckle gem

Original

def is_odd?(number) if number % 2 == 0 return true else return false endend

assert is_foo?(2)

Mutation 1

def is_odd?(number) if number % 2 == 0 return false else return true endend

assert is_foo?(2)

Mutation 2

def is_odd?(number) if nil % 2 == 0 return true else return false endend

assert is_foo?(2)

Code complexityUsing flog gem

test.rb

class Test def blah a = eval “1+1” if a == 2 puts “yay” end endend

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

Comparative quality

Mephisto 0.8 Typo 5.0.3

article.rb

tag.rb

user.rb

325 574

97 67

124 81

Cyclomatic complexityUsing saikuro gem

Cyclomatic complexity

• Academic, formal

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

Comparative quality

Mephisto 0.8 Typo 5.0.3

article.rb

tag.rb

user.rb

67 124

17 16

25 24

flog vs. saikuro

• Cyclometic complexity is disputed

• Flog is not academically proven

• Flog has better Ruby understanding

Tracking over time

• Snapshot metrics not very useful

• Comparisons very difficult

• Tracking over time spots problems

• Use CruiseControl.rb plus metric_fu

Questions

http://www.nedforce.nl