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'], // Relative paths from contractsDir
  skipTests: ['testFileName.js'], // Relative paths from testDir
  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}
}