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Version: v1.3

Testing Smart Contracts

Once you have deployed a smart contract on a public network, altering it to fix an error can be hard, and it goes against the principle of immutability, which can create trust issues with users. And, even if it were simple, you could only fix an error or vulnerability after it is discovered. So, your contract and its users may be at risk if a third party detects a vulnerability before you do.

The best way to avoid these overheads and vulnerabilities is to test your contracts thoroughly before deploying them. You can use unit and integration tests, as well as manual testing, to ensure your contracts behave as expected.

Automated Testing

You can use various tools to automatically test your smart contract’s code and for any error in execution. The great benefit of automated testing is that it requires minimal human intervention, and it can be built right into your deployment pipelines.

Automated testing also allows you to run repetitive and time-consuming tasks without testing each case manually and avoid human errors, which can happen when you manually input tons of data.

However, you must be careful, as automated testing can lead to false positives or miss certain edge cases.

Unit Tests

In a nutshell, unit testing ensures that each function and component works correctly by evaluating each independently. You can use unit tests to ensure that functions return the expected values and modify your contract's state properly. They should be simple, quick to run and provide helpful feedback if anything goes wrong. This makes them an ideal tool to ensure your contracts run smoothly after any modifications.

Unit Testing Guidelines

Understand the logic behind your contract’s workflow

Before you can write any tests, you should understand how your contract is supposed to behave. You should know its functionalities and how users will access them. Your tests should cover different functions a user may call when interacting with the contract and check that functions are disabled when they should be.

Evaluate your contract’s assumptions

It is important to verify that every internal decision the contract takes matches your assumptions on how it should behave. This forces you to think about edge cases rather than only thinking of the “happy path” you want your users to take. You can write negative tests to assert how your contract would respond to invalid or malicious inputs.

Measure Code Coverage

Code coverage is a key metric when it comes to understanding the effectiveness of your tests. It measures the number of lines, statements, and branches that are actually executed during your unit tests. If you don’t have thorough code coverage, your test may give what is commonly known as a “false negative”, where your contract passed all your tests, but your tests didn’t evaluate all the possible vulnerabilities.

Unit Testing Frameworks

The quality of your unit test will depend on the quality of the tools you use to write and execute them. You should use a testing framework that is regularly maintained and updated, provides features that are relevant to your contract, and is popular amongst other developers.


If you want to test ISC-specific functionalities, like the magic contract, you should use the Solo Framework.

Integration Tests

Integration tests are beneficial when your contract adopts a modular architecture or interfaces with other contracts during its execution. While unit tests focus on testing functions in isolation, trying each cog in the machine individually, so to speak, integration tests evaluate how these functions work together as a whole, testing the machine as a whole. You should use integration tests to detect any issues arising from interactions between different functions in your contracts' cross-contract calls and ensure that inherited or extended functions are working as expected.


You can use the EVM Testnet to conduct integration tests without incurring any fees or the IOTA Sandbox if you want to run the tests locally.

Manual Testing

Once you have a complete batch of automated tests, manually testing your contract to ensure it behaves as expected in the real world is still good practice. However, to avoid incurring fees or deploying a faulty contract, you can manually test your contract using a sandboxed local network and the EVM Testnet.

Testing using the IOTA Sandbox serves well for the first stage of automated and manual integration tests, as you have complete control over the entire local network. Once you are confident about how your contract behaves locally, you can deploy and test on the EVM Testnet, which replicates the IOTA EVM and ShimmerEVM networks, but also enables cost and risk-free interactions.