mutation testing with pit (booster 2014, 2014-mar-13)
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© Computas AS 11.03.14
Mutation Testing with PIT
Filip van LaenenBooster 20142014-03-13
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Agenda
• Basics of mutation testing• Relation to other testing techniques• Example• Mutation testing techniques• Mutation testing tools• Personal experiences and recommendations
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Basics ofMutation Testing
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Mutation Testing in a Nutshell
Seeking The Summoner @ The Daily WTFhttp://thedailywtf.com/Articles/Seeking-The-Summoner.aspx
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Mutation Testing in a Nutshell (cont'd)
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Mutation Testing in a Nutshell (cont'd)
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Mutation Testing in a Nutshell (cont'd)
• Unit tests guard the source code• But who guards the guardians?
• Do the unit tests cover all source code?• Lines?• Branches?• Paths?
• Do the unit tests test the right things?
Mutation testing tests the tests!
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Mutation Testing in a Nutshell (cont'd)
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Mutation Testing in a Nutshell (cont'd)
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Mutation Testing in a Nutshell (cont'd)
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Mutation Testing in a Nutshell (cont'd)
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Mutation Testing in a Nutshell (cont'd)
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Mutation Testing in a Nutshell (cont'd)
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Mutation Testing in a Nutshell (cont'd)
int max(int a, int b) { return (a < b) ? b : a;}
int max(int a, int b) { return (a <= b) ? b : a;}
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Mutation Testing in a Nutshell (cont'd)
“
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Does Mutation Testing Work?
In practice, if the software contains a fault, there will usually be a set of
mutants that can only be killed by a test case that also detects that fault.
Geist et. al., “Estimation and Enhancement of Real-time Software Reliability through Mutation Analysis,” 1992
“
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Does Mutation Testing Work? (cont'd)
Complex faults are coupled to simple faults in such a way that a test data set
that detects all simple faults in a program will detect most complex faults.
K. Wah, “Fault Coupling in Finite Bijective Functions,” 1995
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Does Mutation Testing Work? (cont'd)
• “Generated mutants are similar to real faults.”• Andrews, Briand, Labiche, ICSE 2005
• “Mutation testing is more powerful than statement or branch coverage.”• Walsh, Ph.D. Thesis, State University of New York at
Binghampton, 1985• “Mutation testing is superior to data flow
coverage criteria.”• Frankl, Weiss, Hu, Journal of Systems and Software,
1997
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Relation to OtherTesting Techniques
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Relation to Other Testing Techniques
• Unit tests• Test-Driven Development (TDD)• Test coverage• Static code analysis• Fuzz testing
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Relation to Other Testing Techniques
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Is Mutation Testing New?
• R. Lipton, “Fault Diagnosis of Computer Programs,” 1971
• R. Lipton et. al., “Hints on Test Data Selection: Help for the Practicing Programmer,” 1978
• Historical obstacles:• No unit testing• No TDD• Inefficient implementation
• Hence time-consuming• No integration with IDEs
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Practical Exampleof Mutation Testing
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Code Along…
https://github.com/computas-fvl/booster2014
git clone \https://github.com/computas-fvl/booster2014.git
mvn clean site:site \ org.pitest:pitest-maven:mutationCoverage
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Mutation TestingTechniques
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Mutation Testing Techniques
• Three aspects:• Mutation injection• Mutation types• Unit test selection per mutant
• Key properties:• Efficiency• Performance
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Mutation Injection
• Source code mutation• Binary code mutation• Caveats:
• De-mutation• Compilation errors• Invalid binary code
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Mutation Types
• Some mutations never change behaviour• Constants reused by unit tests• Log messages
• Some mutations can change behaviour• Switching between < and ≠• Switching between < and ≤
• Some mutations always change behaviour• Switching between < and ≥
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Mutation Types (cont'd)
int max(int a, int b) { return (a < b) ? b : a;}
int max(int a, int b) { return (a <= b) ? b : a;}
int max(int a, int b) { return (a >= b) ? b : a;}
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Mutation Types (cont'd)
for (int i = 0; i < 10; i++) …
for (int i = 0; i != 10; i++) …
for (int i = 0; i >= 10; i++) …
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Mutation Types Guaranteed to Change Behaviour
• Negation of the comparison• Switching between = and ≠• Switching between < and ≥• Switching between > and ≤
• Negation of boolean conditions• Adding a ¬, ! or ~
• Shortcutting boolean conditions• Replacement with True or False
*
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Unit Test Selection
• Goal: find the unit test that “kills” the mutant• Selection aids:
• Hints• Name/package matching• Code coverage tools• Automatic learning• Other heuristics
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Unit Test Selection (cont'd)
• System:• 50 classes• 20 unit tests per class• 1 ms per unit test• Unit testing time: 50 × 20 × 1ms = 1s
• 10 mutants per class:• Brute-force: 10 × 50 × 1s = 6m 20s• Educated: 10 × 50 × 20 × 1ms = 10s
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Unit Test Selection (cont'd)
• System:• 500 classes• 20 unit tests per class• 1 ms per unit test• Unit testing time: 500 × 20 × 1ms = 10s
• 10 mutants per class:• Brute-force: 10 × 500 × 10s = 13h 53m 20s• Educated: 10 × 500 × 20 × 1ms = 1m 40s
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Complexity
• f: Number of function points• φ: Number of function points per class, ≥ 1• τ: Number of unit tests per function point, ≥ 1• μ: Number of mutants per function point, ≥ 1
• Brute-force: (f × τ) × (f × μ) = τ × μ × f²• Educated force: τ × μ × φ × f• Ideal: τ × μ × f
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Complexity (cont'd)
• c: Number of classes• φ: Number of function points per class, ≥ 1• τ: Number of unit tests per function point, ≥ 1• μ: Number of mutants per function point, ≥ 1
• Brute-force: (f × τ) × (f × μ) = τ × μ × φ² × c²• Educated force: τ × μ × φ² × c• Ideal: τ × μ × φ × c
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Loops
for (int i = 0; i < 10; i++) …
for (int i = 0; i < 10; i--) …
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Infinite Loops
• Terminate mutants that take too long to run• What's “too long”?
• Ruins the performance• Can be hard to predict
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Other Problems
• Recursion:• Stack overflows• Out of memory exceptions
• Syntax errors• Segmentation faults
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Mutation TestingTools
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Mutation Testing Tools
• Java:• PIT• Jester (Nester, Pester)• Jumble
• Ruby:• Mutant• Heckle
• C#:• NinjaTurtles
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PIT
• Java• Junit & TestNG• Maven or command-line• Operates on byte code• Large set of mutators
• Also possibly equivalent mutators available• Highly configurable• Sensible defaults
• http://pitest.org/
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PIT Mutators
• Conditionals Boundary• Negate Conditionals• Remove Conditionals*• Math• Increments• Invert Negatives• Inline Constant*• Return Values• Void Method Calls• Non Void Method Calls*• Constructor Calls*
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PIT Sample Report
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Jester
• Java• JUnit• Usually run from the command-line
• Grester for Maven2• Operates on source code• Runs all unit tests on all classes• Reporting and documentation could be better
• http://jester.sourceforge.net/• http://sourceforge.net/projects/grester/
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Jester Sample Report Overview
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Jester Sample Detailed Report
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Pester and Nester
• Pester• Jester for Python• PyUnit
• Nester• Port of Jester for C#• NUnit• Integrated with Visual Studio• But outdated…• http://nester.sourceforge.net/
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Nester Sample Report
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Jumble
• Java• JUnit• Run from the command-line• Operates on byte code• Runs unit tests on a class• Reporting and documentation could be better• Claims to be faster than Jester
• http://jumble.sourceforge.net/index.html
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Jumble Sample Report
Mutating FooTests: FooTestMutation points = 12, unit test time limit 2.02s..M FAIL: Foo:31: negated conditionalM FAIL: Foo:33: negated conditionalM FAIL: Foo:34: - -> +M FAIL: Foo:35: negated conditional......Score: 67%
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Mutant
• Ruby 1.9 and 2.0• rspec2• Usually run from the command-line• Good to-the-point reporting• Good performance• OK documentation• Active project
• https://github.com/mbj/mutant
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Heckle
• Ruby 1.8• Doesn't work on Ruby 1.9
• Test::Unit and rSpec• Usually run from the command-line• Runs a set of unit tests on a class or a method• Good to-the-point reporting• Good performance• Virtually no documentation
• http://rubyforge.org/projects/seattlerb/• http://docs.seattlerb.org/heckle/
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Heckle Mutations
• Booleans• Numbers• Strings• Symbols• Ranges• Regexes• Branches (if, while, unless, until)
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NinjaTurtles
• .Net:• C#• Visual Basic/VB.NET• Any other .NET language code
• Doesn't seem much alive
• http://www.mutation-testing.net/
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NinjaTurtles Mutations
• Sequence point deletion• Arithmetic operator substitution (*, /, +, -, %)• Bitwise operator substitution (&, |, ^)• Branch substituion (condition, always and never
branch)• Conditional boundary substition (< and <=, >
and >=)• Substitution of reads from variables,
parameters and fields of the same type• Substitution of writes to variables of the same
type
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Personal Experiencesand Recommendations
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Experiences and Recommendations
• Use mutation testing from day 1• Start on a small code base
• Keep number of unit tests per class low• Have small classes
• Select a good tool• Configurable• Flexible• One that can output the mutant
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Experiences and Recommendations (cont'd)
• Believe the tool• Or try to proof that the tool is wrong
• Fix the problem• Don't turn mutation testing off
• Embrace the “more than 100%” test coverage• Path coverage• Less code• More unit tests• More intelligent unit tests
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Improvements
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Improvements
• Integration with more unit testing frameworks• Better unit test–source code mapping
• Better heuristics• Parallellisation• Better reporting• IDE integration• Building tool integration
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Questions?
Computas ASLysaker Torg 45, pb 482N-1327 LysakerNORWAY
Tel +47-67 83 10 00Fax +47-67 83 10 01Org.nr: NO 986 352 325 MVAwww.computas.com
Contact:
[email protected] @filipvanlaenen