Flow Playground

Smart Contract Testing Guidelines

Achieving good test coverage is vital for assuring the quality of code written to be deployed on the Flow blockchain.

Automated tests can be run locally in the Flow emulator, and on the Flow testnet. These tests should include both unit tests; to exercise each feature of a contract, and integration tests; to exercise the behaviour of different parts of the project as a whole.

Human-driven tests, in which individual testers work manually through user stories via the project's user interface or custom transactions, can also be performed locally. Tests with groups of testers can be performed similarly on testnet in a similar manner.

Finally, unstructured closed testing with a limited audience on testnet can gain valuable information about performance and security by capturing usage data from more organic interaction with the project's smart contracts over days or weeks.

Testing Requirements

For code that is being evaluated for deployment on the Flow mainnet, Dapper Labs requires the following be included in the code repository that we receive containing the smart contracts to be reviewed:

  • Every publicly exposed feature of a contract and its resources should have unit tests that check both for success with correct input and for failure with incorrect input. These tests should be capable of being run locally with the Flow emulator, with no or minimal extra resources or configuration, and with a single command.
  • Each user story or workflow that uses the smart contracts should have an integration test that ensures that the series of steps required to complete it does so successfully with test data.

For manual testing prior to approval for deployment to mainnet the code must be deployed on testnet and used for two weeks. This is to test the code in conditions as close to those it will be used in on mainnet if and when it is deployed there.

Writing Tests

There are official SDKs for Flow in both Go and JavaScript.

In both cases, the code will need to deploy the contracts, configure accounts to interact with them and send transactions to them. It will then have to wait for the transactions to be sealed and check the results by catching exceptions, checking for events, and querying state using scripts.

Go Tests

Tests in Go can be written using flow-go-sdk and the go test command.

You can find examples of Go tests in the following projects:,

Note that these tests are tied to the emulator but it is simple to refactor tests to run on testnet as well.

JavaScript Tests

Tests in JavaScript can be written using fcl and flow-js-testing.

flow-js-testing is a newer addition so we do not have any examples using it yet.