SuMo

SuMo is a mutation testing tool for Solidity Smart Contracts. It features 25 Solidity-specific mutation operators, as well as 19 traditional operators.

SuMo was designed to run mutation testing on Solidity projects in a NodeJS environment. It can run test using Truffle, Hardhat, Brownie and Forge. If needed, SuMo can also automatically spawn Ganache instances to guarantee a clean-room testing environment between mutants.

Table of Contents

• Installation
• Configuration
• CLI Usage
• Trivial Compiler Equivalence
• Mutation Operators
• Publications

Installation

To install sumo run npm install @morenabarboni/sumo

Configuration ⚙️

Before using SuMo you must specify your desired configuration in a sumo-config.js in the root directory of your project. The sumo-config.js is automatically generated upon installation.

Here's a simple example of sumo-config.js:

module.exports = {
  buildDir: 'build',
  contractsDir: 'contracts',
  testDir: 'test',
  skipContracts: ['contractName.sol'],
  skipTests: ['testDir/testFileName.js'],
  testingTimeOutInSec: 300,
  network: "none",
  testingFramework: "truffle",
  minimal: false,
  tce: false
}

1) SUT directories

These (optional) fields identify relevant project directories.

Field	Description	Default Value
contractsDir	relative path to the directory of the contracts to be mutated	contracts
testDir	relative path to the directory of the tests to be evaluated	test/tests
buildDir	relative path to the directory of the compilation artifacts	build/out/artifacts

2) Mutation Process

These fields allow to configure the mutation testing process:

Field	Description	Default Value
minimal	use minimal mutation rules	false
skipContracts	blacklist of relative paths to contract files (or folders)	[]
skipTests	blacklist of relative paths to test files (or folders)	[]
tce	use the Trivial Compiler Equivalence	false
testingTimeOutInSec	seconds after which a mutant is marked as timed-out during testing	300

3) Testing Interface

These fields specify what testing framework and blockchain simulator SuMo should use to conduct mutation testing:

Field	Description	Available Options	Default Value
network	the blockchain simulator to be used	ganache, none	none
testingFramework	the testing framework to be used for compiling and testing the smart contracts	brownie, forge, hardhat, truffle, custom	truffle

Truffle and Hardhat

When choosing truffle or hardhat:

• SuMo will rely on the local truffle or hardhat package installed in the project;
• The smart contracts will be compiled with a minimal compile command (e.g., truffle compile );
• The smart contracts will be tested with a minimal test command followed by the bail argument, and (optionally) by a list of test files to be executed (e.g., truffle test ...testFiles -b) .

Brownie

When choosing brownie:

• SuMo will rely on a local/global brownie installation;
• The smart contracts will be compiled with a minimal compile command (e.g., brownie compile );
• The smart contracts will be tested with a minimal test command followed by the exitfirst argument, and (optionally) by a list of test files to be executed (e.g., brownie test ...testFiles --exitfirst) .

Forge

When choosing forge :

• SuMo will rely on the global installation of foundry;
• The smart contracts will be compiled with a minimal compile command (e.g., forge build);
• The smart contracts will be tested with a minimal test command followed by the fail-fast argument, and (optionally) by a list of test files to be executed (e.g., forge test ...testFiles --fail-fast).
• Make sure that your forge installation is up-to-date to enable --fail-fast.

Custom

• When choosing custom:
  • SuMo will invoke the compile and test script defined in your package.json. This allows you to customize both scripts and have more control over the testing process;
  • The skipTests list will be overridden by the test script in your package.json. To skip some test files, you can either: 1) append the specific test files you want to run to your test script, or 2) remove the test files to be skipped from the test folder.
  • The --bail/--exitfirst/--fail-fast option should be added to the test script to speed up mutation testing.

CLI Usage

Selecting the Mutation Operators

Before starting the mutation process you can choose which mutation operators to use:

Command	Description	Usage	Example
list	Shows the enabled mutation operators.	npx/yarn sumo list	$ npx sumo list
enable	Enables one or more mutation operators. If no operator IDs are specified, all of them are enabled.	npx/yarn sumo enable [...ID]	$ npx sumo enable $ npx sumo enable AOR BOR
disable	Disables one or more mutation operators. If no operator IDs are specified, all of them are disabled.	npx/yarn sumo disable [...ID]	$ npx sumo disable $ npx sumo disable FVR

Viewing the available mutations

Command	Description	Usage	Example
lookup	Generates the mutations and saves them to ./sumo/generated.csv without starting mutation testing.	npx/yarn sumo lookup	$ npx sumo lookup
mutate	Generates the mutations and saves a copy of each .sol mutant to to ./sumo/mutants.	npx/yarn sumo mutate	$ npx sumo mutate

Running Mutation Testing

Command	Description	Usage	Example
pretest	Runs the test suite on the original smart contracts to check if all tests pass and can be successfully evaluated. Pretest is automatically run when sumo test is executed.	npx/yarn sumo pretest	$ npx sumo pretest
test	Starts the mutation testing process. You can also choose a single mutant / an interval of mutants to be tested by sepcifying <startHash> and (optionally) <endHash>.	npx/yarn sumo test <startHash> <endHash>	$ npx sumo test $ npx sumo test mbc5e8f56 mbg5t86o6
restore	Restores the SUT files to a clean version. This should be executed if you suddenly interrupt the mutation process. Note that the restore command overwrites your codebase with the files stored in the sumo/baseline folder. If you need to restore the project files, make sure to do so before performing other operations as the baseline is automatically refreshed on subsequent preflight or test runs.	$ npx/yarn sumo restore	$ npx sumo restore

Viewing the results

SuMo automatically creates a sumo\results folder in the root directory of the project with the following reports:

• operators.xlsx Results of the mutation testing process grouped by operator
• results.csv Results of the mutation testing process for each mutant. This synchronous log is updated each time a mutant is assigned a status
• sumo-log.txt Logs info about the mutation testing process
• \mutants Mutated .sol contracts generated with sumo mutate

Trivial Compiler Equivalence

The Trivial Compiler Equivalence compares the smart contract bytecode to detect equivalences between mutants and it can only work if:

1. the solc compiler optimization is enabled;
2. no metadata hash is appended to the contract bytecode.

1) TCE for Truffle and Hardhat

If your testingFramework is truffle or hardhat, you must add the following to your truffle-config.js or hardhat.config.js file:

 compilers: {
    solc: {
        optimizer: {
            enabled: true,
            runs: 200
            ...
        },
        metadata: {
              bytecodeHash: "none"
        }
      }
  }

2)TCE for Brownie

If your testingFramework is brownie, you must add the following to your brownie-config.yaml file:

compiler:
    solc:
        optimize: true
        runs: 200

3) TCE for Forge

If your testingFramework is forge you must add the following to your foundry.toml file:

optimizer = true
optimizer-runs = 200

4) TCE for Hybrid Test Suites

If your testingFramework is custom but you still rely on a single testing framework you can refer to the previous sections.

However, if you are using custom to evaluate hybrid test suites (e.g., forge and hardhat) you must make sure that the sumo configuration is consistent.

For example, consider the following package.json scripts:

 scripts: {
    compile: "hardhat compile",
    test "hardhat test --bail && forge test --fail-fast"
 }

If you make SuMo use hardhat to compile the contracts, make sure that the buildDir points to the hardhat compiled artifacts and not to the forge ones, and vice versa.

Mutation Operators 👾

SuMo includes currently 25 Solidity-specific operators and 19 Traditional operators.

Minimal Mutation Rules

Some mutation operators foresee a minimal version:

• The extended operators are composed of mutation rules capable of generating a more comprehensive collection of mutants. These operators guarantee higher reliability at the price of a more expensive and time-consuming mutation testing process.
• The minimal operators consist of simplified rules that aim to limit the generation of likely subsumed mutants and speed up the testing process.

By default, SuMo employs the extended operators. However, you can enable the minimal rules from the sumo-config.js file.

Traditional Mutation Operators

Operator	Name	Mutation Example	Minimal version available
ACM	Argument Change of overloaded Method call	overloadedFunc(a,b); → overloadedFunc(a,b,c);	N
AOR	Assignment Operator Replacement	+= → =	Y
BCRD	Break and Continue Replacement and Deletion	break → continue → break	N
BLR	Boolean Literal Replacement	true → false	N
BOR	Binary Operator Replacement	+ → - < → >=	Y
CBD	Catch Block Deletion	catch{} →	N
CSC	Conditional Statement Change	if(condition) → if(false) else{} →	N
ER	Enum Replacemet	enum.member1 → enum.member2	Y
ECS	Explicit Conversion to Smaller type	uint256 → uint8	N
HLR	Hexadecimal Literal Replacement	hex\"01\" → hex\"random\"	N
ICM	Increments Mirror	-= → =-	N
ILR	Integer Literal Replacement	1 → 0	N
LCS	Loop Statement Change	while(condition) → while(false)	N
OLFD	Overloaded Function Deletion	function overloadedF(){} →	N
ORFD	Overridden Function Deletion	function f() override {} →	N
SKI	Super Keyword Insertion	x = getData() → x = super.getData()	N
SKD	Super Keyword Deletion	x = super.getData() → x = getData()	N
SLR	String Literal Replacement	"string" → ""	N
UORD	Unary Operator Replacement and Deletion	++ → -- ! →	N

Solidity Mutation Operators

Operator	Name	Mutation Example	Minimal version available
AVR	Address Value Replacement	0x67ED2e5dD3d0... → address.this()	N
CCD	Contract Constructor Deletion	constructor(){} →	N
DLR	Data Location Keyword Replacement	memory → storage	N
DOD	Delete Operator Deletion	delete →	N
ETR	Ether Transfer function Replacement	delegatecall() → call()	N
EED	Event Emission Deletion	emit Deposit(...) → /*emit Deposit(...)*/	N
EHC	Exception Handling Change	require(...) → /*require(...)*/	N
FVR	Function Visibility Replacement	function f() public → function f() private	Y
GVR	Global Variable Replacement	msg.value() → tx.gasprice()	Y
MCR	Mathematical and Cryptographic function Replacement	addmod → mulmod keccak256 → sha256	N
MOD	Modifier Deletion	function f() onlyOwner → function f()	Y
MOI	Modifier Insertion	function f() → function f() onlyOwner	Y
MOC	Modifier Order Change	function f() modA modB → function f() modB modA	Y
MOR	Modifier Replacement	function f() onlyOwner → function f() onlyAdmin	Y
OMD	Overridden Modifier Deletion	modifier m() override {} →	N
PKD	Payable Keyword Deletion	function f() payable → function f()	N
RSD	Return Statement Deletion	return amount; → //return amount;	N
RVS	Return Values Swap	return (1, "msg", 100); → return (100, "msg", 1);	Y
SFD	Selfdestruct Deletion	selfdestruct(); → //selfdestruct();	N
SFI	Selfdestruct Insertion	doSomething; selfdestruct(); → selfdestruct(); doSomething;	N
SFR	SafeMath Function Replacement	SafeMath.add → SafeMath.sub	Y
SCEC	Switch Call Expression Casting	Contract c = Contract(0x86C9...); → Contract c = Contract(0x67ED...);	N
TOR	Transaction Origin Replacement	msg.sender → tx.origin	N
VUR	Variable Unit Replacement	wei → ether minutes → hours	Y
VVR	Variable Visibility Replacement	uint private data; → uint public data;	Y

Publications

To cite SuMo, please use the following:

@article{BARBONI2022111445,
  title = {SuMo: A mutation testing approach and tool for the Ethereum blockchain},
  journal = {Journal of Systems and Software},
  volume = {193},
  pages = {111445},
  year = {2022},
  issn = {0164-1212},
  doi = {https://doi.org/10.1016/j.jss.2022.111445},
  author = {Morena Barboni and Andrea Morichetta and Andrea Polini}
}