Fuzzing (or Fuzz Testing) is a technique to verify the robustness of a program-under-test. Valid input is replaced by random values with the goal to force the program-under-test into unresponsive states. In this position paper, we propose a white box Fuzzing approach by transforming (mutating) existing test methods. We adopt the mechanisms used for test amplification to generate crash inducing tests, which developers can reproduce later. We provide anecdotal evidence that our approach towards Fuzzing reveals crashing issues in the Pharo environment.

1. Universiteit Antwerpen
Reproducible Crashes:
Fuzzing Pharo by Mutating the Test
Methods
Mehrdad Abdi — Henrique Rocha — Serge Demeyer
VST 2021 (March 9th)

2. VST2021 © Serge Demeyer
• Background
- Fuzzing
- Mutation Coverage
- Test Amplification
• Fuzzing by amplification
- Motivating examples
- Proposed approach
- Challenge
• Conclusions
Outline
2

3. Fuzz
Testing
Mutation
Coverage
Test
Amplification

4. VST2021 © Serge Demeyer
Testing
4
Program
Under
Test
Valid Input
Expected output
Software Testing is the process of executing a program or system with
the intent of finding errors.
(Myers, Glenford J., The art of software testing. Wiley, 1979

5. VST2021 © Serge Demeyer
Fuzz Testing
5
Program
Under
Test
Unexpected Input
Crash/Freeze
Fuzzing (or Fuzz Testing) is an automated testing technique to verify the
robustness of a program-under-test.
Valid input is replaced by random values with the goal to force the
program-under-test into unexpected exceptional behavior.

6. VST2021 © Serge Demeyer
Black Box Fuzzing
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Access to
execution
Mutating valid
inputs

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White Box Fuzzing
7
Access to code,
models, specs, …
Program Analysis

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Grey Box Fuzzing
8
Limited Access
(bytecode, trace, …)
Reverse
Engineering

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Code Coverage
9
Program
Under
Test
Valid Input Expected output
coverage

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Line Coverage (Statement / Branch / Path / …)
10
c++
java

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Mutation Testing
11
int compare(int v1,
int v2)
{if (v1 <v2)
return 1;
return -1
;
}
int compare(int v1,
int v2)
{if (v1 >=v2)
return 1;
return -1
;
}
🙂
🙁

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Mutation Coverage
12

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Test Amplification
13
Program
Under
Test
Valid Input Expected output
coverage
+coverage
Extra Input
Extra Input
+Extra Input +Extra output

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Test amplification Definition
14
[Danglot-19] Benjamin Danglot, Oscar Vera-Perez, Zhongxing Yu, Andy Zaidman, Martin Monperrus and Benoit
Baudry. 2019. A snowballing literature study on test ampli
fi
ca
ti
on. Journal of Systems and Software.
Test amplification consists of exploiting the knowledge of a large
number of test cases, in which developers embed meaningful
input data and expected properties in the form of oracles, in
order to enhance these manually written tests with respect to
an engineering goal. [Danglot-19]
mutation coverage

15. VST2021 © Serge Demeyer
Fuzzing by Amplification
15
[Danglot-19] Benjamin Danglot, Oscar Vera-Perez, Zhongxing Yu, Andy Zaidman, Martin Monperrus and Benoit
Baudry. 2019. A snowballing literature study on test ampli
fi
ca
ti
on. Journal of Systems and Software.
Test amplification consists of exploiting the knowledge of a large
number of test cases, in which developers embed meaningful
input data and expected properties in the form of oracles, in
order to enhance these manually written tests with respect to
an engineering goal. [Danglot-19]
Detecting unexpected terminations
(crashes, freezes, …)

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Fuzzing by Amplification
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Image from: https://www.enwild.com/snow-peak-colored-titanium-spork.html
Fuzzing?
Amplification?

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Motivating example (1/2)
17

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Motivating example (2/2)
18

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Proposed approach
19
Profile Test Method

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Proposed approach
20
(2) Assertion Removal

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Proposed approach
21
(2) Input Amplification
Input Amplification Operators
• Literal mutation
• Nullify objects
• Remove statements
• Duplicate statements
• Add new statements
• Change helper methods
• …

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Proposed approach
22
(3) Create new tests
+ install in the test suite

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Proposed approach
23
(4) Execute

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Proposed approach
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(5) Sandboxing

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Proposed approach
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Observation

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Proposed approach
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(6) Reporting

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Challenge
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If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

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Challenge
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Explicit
Types
Profiling
White Box Fuzzing

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Smalltalk Community
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Cool dude!
Mehrdad Abdi, Henrique Rocha, and Serge Demeyer. Reproducible crashes: Fuzzing pharo
by mutating the test methods. In Proceedings IWST 2020 (International Workshop on
Smalltalk Technologies). ESUG, 2020.

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Testing Community
30
Related Work?
• Fuzzing by mutating test code
• Fuzzing / Test Amplification
- dynamically typed languages
(Python, Javascript, …)
feedback and/or suggestions
serge.demeyer@uantwerpen.be