Benoit Baudry (KTH) presentation at EclipseCon'17

1. Mutate and Test Your Tests
Benoit Baudry
KTH, Sweden
1
baudry@kth.se

2. Test Your Tests
•What do you expect from test cases?
• Cover requirements
• Stress the application
• Prevent regressions
• Reveal bugs
Benoit Baudry, KTH, EclipseCon'17
2

3. Test Your Tests
•What do you expect from test cases?
• Cover requirements
• Stress the application
• Prevent regressions
• Reveal bugs
Benoit Baudry, KTH, EclipseCon'17
3

4. 4
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs);
}
Benoit Baudry, KTH, EclipseCon'17

5. long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
5
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs);
}
Benoit Baudry, KTH, EclipseCon'17

6. Coverage
long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
6
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs);
}
Benoit Baudry, KTH, EclipseCon'17

7. Coverage
7
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs);
}
@Test
factorialWith5Test() {
assertEqual(1, fact(0));}
long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
Benoit Baudry, KTH, EclipseCon'17

8. 8
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs);
}
@Test
factorialWith5Test() {
assertEqual(1, fact(0));}
long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
Are these test cases good at
detecting bugs?
Benoit Baudry, KTH, EclipseCon'17

9. 9
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs);
}
@Test
factorialWith5Test() {
assertEqual(1, fact(0));}
long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
Are these test cases good at
detecting bugs?
Let’s mutate our code to see.
Benoit Baudry, KTH, EclipseCon'17

10. Mutation analysis
•Tests are good if they can detect bugs
•Principle: generate bugs and test the tests
10
Benoit Baudry, KTH, EclipseCon'17

11. Mutation analysis
•Tests are good if they can detect bugs
•Principle: generate bugs and test the tests
•Mutation operators
•Mutant = Program with one mutation
11
Benoit Baudry, KTH, EclipseCon'17

12. Mutation analysis
Inputs : P, TS, Ops
Output : score, coverage
M <- generateMutants (P, OPs)
forAll (m in M)
run (TS,m)
if (one-test-fail)
then killed <- m
else alive <- m
score = killed / size(M)
12
Benoit Baudry, KTH, EclipseCon'17

13. PIT
•Open source
•Actively developed and maintained
•State of the art
•For Java
•Integrates with major build systems
13
Benoit Baudry, KTH, EclipseCon'17

14. PIT mutation operators
•Conditions
•Constants
•Return
•Delete method calls
•Constructor call
14
Benoit Baudry, KTH, EclipseCon'17

15. long fact(int n) {
if(n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
15
Benoit Baudry, KTH, EclipseCon'17

16. long fact(int n) {
if(n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
16
n != 0 return 1+1
< --!(i<=n)
result/i
result+1
Benoit Baudry, KTH, EclipseCon'17

17. long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
17
n != 0 return 1+1
< --!(i<=n)
result/i
result+1
Benoit Baudry, KTH, EclipseCon'17

18. long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
18
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs); }
Benoit Baudry, KTH, EclipseCon'17
n != 0 return 1+1
< --!(i<=n)
result/i
result+1

19. long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
19
@Test
factorialWith5Test() {
assertEqual(1, fact(0));}
Benoit Baudry, KTH, EclipseCon'17
n != 0 return 1+1
< --!(i<=n)
result/i
result+1

20. long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
20
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs); }
@Test
factorialWith5Test() {
assertEqual(1, fact(0));}
Benoit Baudry, KTH, EclipseCon'17
n != 0 return 1+1
< --!(i<=n)
result/i
result+1

21. long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
Mutation reveals bugs in the test suite
21
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs); }
@Test
factorialWith5Test() {
assertEqual(1, fact(0));}
Benoit Baudry, KTH, EclipseCon'17
Bugs in the test suite:
- Weak oracle
- Missing input
n != 0 return 1+1
< --!(i<=n)
result/i
result+1

22. long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
22
@Test
factorialWith5Test() {
long obs = fact(5);
assertEqual(120, obs); }
@Test
factorialWith5Test() {
assertEqual(1, fact(0));}
@Test
factorialWith1Test() {
assertEqual(1, fact(1));}
Benoit Baudry, KTH, EclipseCon'17
n != 0 return 1+1
< --!(i<=n)
result/i
result+1

23. PIT – reporting
23
Benoit Baudry, KTH, EclipseCon'17

24. PIT – reporting
24
Benoit Baudry, KTH, EclipseCon'17

25. Project #LOC #Mutants Time (h) Score (%)
Amazon Web Services SDK 1703892 2141690 04:25:35 76.28
XWiki Rendering Engine 104727 112609 01:59:55 50.89
Apache Commons Math 180951 104786 03:22:18 83.81
JFreeChart 134353 89592 00:41:28 58.04
Apache PdfBox 137099 79763 06:20:25 58.89
Java Git 128874 78316 16:02:00 73.86
SCIFIO 55347 62768 03:12:11 45.92
Joda-Time 85911 31233 00:16:32 81.65
Apache Commons Lang 60733 30361 00:21:02 86.17
Apache Commons Collections 51632 20394 00:05:41 85.94
Urban Airship Client Library 40885 17345 00:11:31 82.26
SAT4J 26415 17067 11:11:04 68.58
ImageJ Common 23868 15592 00:29:09 54.77
jsoup 17839 14054 00:12:49 78.34
Jaxen XPath Engine 21204 12210 00:24:40 67.13
Apache Commons Codec 17267 9233 00:07:57 87.82
Apache Commons IO 24334 8809 00:12:48 84.73
Google Gson 20068 7353 00:05:34 81.76
AuthZForce PDP Core 16602 7296 01:23:50 88.18
Apache Commons CLI 7005 2560 00:01:26 88.71
JOpt Simple 9214 2271 00:01:36 93.52Benoit Baudry, KTH, EclipseCon'17
25

26. Descartes
•Mutation operators: extreme mutation
•Active development
•Open source
•Compared to PIT
• Less mutants
• Different type of feedback
• Same framework
26
Benoit Baudry, KTH, EclipseCon'17

27. long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
Descartes - example
27
Benoit Baudry, KTH, EclipseCon'17

28. long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
Descartes - example
28
long fact(int n){
return 0;}
long fact(int n){
return 1;}
Benoit Baudry, KTH, EclipseCon'17
PIT : 7 mutants
Descartes : 2 mutants

29. Scalability of extreme mutation
Benoit Baudry, KTH, EclipseCon'17
29
public static boolean isValidXmlChar(int ch){
return (ch == 0x9)
|| (ch == 0xA)
|| (ch == 0xD)
|| (ch >= 0x20 && ch <= 0xD7FF)
|| (ch >= 0xE000 && ch <= 0xFFFD
|| (ch >= 0x10000 && ch <= 0x10FFFF);
}
PIT : 45 mutants
Descartes : 2 mutants

30. Project Mutants PIT Mutants Descartes Time PIT Time Descartes
Amazon Web Services SDK 2141690 161758 04:25:35 01:27:30
XWiki Rendering Engine 112609 5534 01:59:55 00:10:50
Apache Commons Math 104786 7150 03:22:18 00:08:30
JFreeChart 89592 7210 00:41:28 00:05:26
Apache PdfBox 79763 7559 06:20:25 00:42:11
Java Git 78316 7152 16:02:00 00:56:07
SCIFIO 62768 3627 03:12:11 00:15:26
Joda-Time 31233 4525 00:16:32 00:04:13
Apache Commons Lang 30361 3872 00:21:02 00:02:18
Apache Commons Collections 20394 3558 00:05:41 00:01:48
Urban Airship Client Library 17345 3082 00:11:31 00:09:38
SAT4J 17067 2296 11:11:04 00:56:42
ImageJ Common 15592 1947 00:29:09 00:04:08
jsoup 14054 1566 00:12:49 00:02:45
Jaxen XPath Engine 12210 1252 00:24:40 00:01:34
Apache Commons Codec 9233 979 00:07:57 00:02:02
Apache Commons IO 8809 1164 00:12:48 00:02:18
Google Gson 7353 848 00:05:34 00:01:11
AuthZForce PDP Core 7296 626 01:23:50 00:08:45
Apache Commons CLI 2560 271 00:01:26 00:00:09
JOpt Simple 2271 412 00:01:36 00:00:25Benoit Baudry, KTH, EclipseCon'17
30

31. Coarser grain than PIT
Benoit Baudry, KTH, EclipseCon'17
31
long fact(int n) {
if (n == 0)return 1;
long result = 1;
for(int i=2; i<=n; i++)
result = result * i;
return result;}
long fact(int n){
return 0;}
long fact(int n){
return 1;}
@Test
factorialWith5Test() {
long obs = fact(5);
assertTrue(5 < obs); }
@Test
factorialWith5Test() {
assertEqual(1, fact(0));}

32. Benoit Baudry, KTH, EclipseCon'17
32
bool equals(object other) {
return other instanceof AClass
&&((AClass) other).aField==aField;
}
bool equals(object other) {
return true;}
bool equals(object other) {
return false;}

33. Benoit Baudry, KTH, EclipseCon'17
33
bool equals(object other) {
return other instanceof AClass
&&((AClass) other).aField==aField;
}
bool equals(object other) {
return true;}
bool equals(object other) {
return false;}
test() {
AClass a = new AClass(3);
AClass b = new AClass(3);
AClass c = new AClass(4);
assertEquals(a, b);
assertFalse(a == c);
}

34. Benoit Baudry, KTH, EclipseCon'17
34
bool equals(object other) {
return other instanceof AClass
&&((AClass) other).aField==aField;
}
bool equals(object other) {
return true;}
bool equals(object other) {
return false;}
test() {
AClass a = new AClass(3);
AClass b = new AClass(3);
AClass c = new AClass(4);
assertEquals(a, b);
assertFalse(a == c);
}

35. Wrong test
Benoit Baudry, KTH, EclipseCon'17
35
bool equals(object other) {
return other instanceof AClass
&&((AClass) other).aField==aField;
}
bool equals(object other) {
return true;}
bool equals(object other) {
return false;}
test() {
AClass a = new AClass(3);
AClass b = new AClass(3);
AClass c = new AClass(4);
assertEquals(a, b);
assertFalse(a == c);
}

36. Benoit Baudry, KTH, EclipseCon'17
36
protected final void prepareSocket(final SSLSocket socket) { }}

37. Benoit Baudry, KTH, EclipseCon'17
37
@Test
void typical() throws NoSuchAlgorithmException {
SdkTLSSocketFactory f = new SdkTLSSocketF(SSLContext.getDefault(),null);
f.prepareSocket(new TestSSLSocket() {
@Override
public void setEnabledProtocols(String[] protocols) {
assertTrue(Arrays.equals(protocols, new String[] {"TLSv1.2", "TLSv1.1", "T
}});}}}
protected final void prepareSocket(final SSLSocket socket) { }}

38. Benoit Baudry, KTH, EclipseCon'17
38
@Test
void typical() throws NoSuchAlgorithmException {
SdkTLSSocketFactory f = new SdkTLSSocketF(SSLContext.getDefault(),null);
f.prepareSocket(new TestSSLSocket() {
@Override
public void setEnabledProtocols(String[] protocols) {
assertTrue(Arrays.equals(protocols, new String[] {"TLSv1.2", "TLSv1.1", "T
}});}}}
protected final void prepareSocket(final SSLSocket socket) { }}

39. Missing oracle
Benoit Baudry, KTH, EclipseCon'17
39
@Test
void typical() throws NoSuchAlgorithmException {
SdkTLSSocketFactory f = new SdkTLSSocketF(SSLContext.getDefault(),null);
f.prepareSocket(new TestSSLSocket() {
@Override
public void setEnabledProtocols(String[] protocols) {
assertTrue(Arrays.equals(protocols, new String[] {"TLSv1.2", "TLSv1.1", "T
}});}}}
protected final void prepareSocket(final SSLSocket socket) { }}

40. Benoit Baudry, KTH, EclipseCon'17
40
private boolean isLongOption(final String token){
if (...){return false;} //Covered 27 times
...
if (...){return true;} //Not covered
else if (...){return true;} //Covered once
return false; //Covered 7 times
}

41. Benoit Baudry, KTH, EclipseCon'17
41
private boolean isLongOption(final String token){
return false;}
private boolean isLongOption(final String token){
return true;}

42. Benoit Baudry, KTH, EclipseCon'17
42
...
if (condition && isLongOption(value)){
action1(value);}
else{
action2(value);}
...
private boolean isLongOption(final String token){
return false;}
private boolean isLongOption(final String token){
return true;}

43. Benoit Baudry, KTH, EclipseCon'17
43
...
if (condition && isLongOption(value)){
action1(value);}
else{
action2(value);}
...
private boolean isLongOption(final String token){
return false;}
private boolean isLongOption(final String token){
return true;}

44. Benoit Baudry, KTH, EclipseCon'17
44
...
if (condition && isLongOption(value)){
action1(value);}
else{
action2(value);}
...
private boolean isLongOption(final String token){
return false;}
private boolean isLongOption(final String token){
return true;}
Testability issue

45. 45
15
285
4 15 54 28 64 132 23
115
14
594 369
92 9 40
158
458 116
65
2592
69
2
14 28 19 27 55
10
17
12
97
85
31 2
14
11
61 20
69
197
274
1516
175 408 1178 610 1840 4245 459
344
585
2931 2237
2596 252 714
456
1726 425
2004
1618
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Tested
Weak pseudo-tested
Strong pseudo-tested
Benoit Baudry, KTH, EclipseCon'17

46. Descartes – future
•Incremental Descartes in the CI
•Github hook
•Support multi module Maven projects
•Enhanced diagnosis
•Integrate into a test augmentation pipeline
Benoit Baudry, KTH, EclipseCon'17
46

47. Conclusion
•Mutation analysis
• Automatic generation of mutants
• Evaluate the test suite
•Bugs in test suites
• Oracle
• Input space coverage
• Testability
• Indirectly tested code
47
Benoit Baudry, KTH, EclipseCon'17

48. Feedback welcome!
• https://github.com/STAMP-project/pitest-descartes
• https://github.com/hcoles/pitest
• http://stamp-project.eu/
baudry@kth.se
48
Benoit Baudry, KTH, EclipseCon'17