Inline configuration for Solidity tests

Hardhat lets you override fuzz and invariant test settings on a per-function basis using NatSpec comments. This is useful when different tests need different parameters. For example, running more fuzz iterations on a critical function, or increasing the depth of an invariant test.

Inline overrides take precedence over the global settings defined in your Solidity tests configuration.

Syntax

Each override is a single line inside a NatSpec comment (line /// or block /** */), following the format hardhat-config: <key> = <value>:

/// hardhat-config: fuzz.runs = 10000
/// hardhat-config: fuzz.maxTestRejects = 500
function testTransferFuzz(uint256 amount) public {
  // ...
}

Block comments are also supported:

/**
 * hardhat-config: invariant.runs = 100
 * hardhat-config: invariant.depth = 50
 * hardhat-config: invariant.failOnRevert = true
 */
function invariantBalanceAlwaysPositive() public {
  // ...
}

Supported configuration keys

Key	Description
fuzz.runs	Number of fuzz iterations to run
fuzz.maxTestRejects	Maximum number of rejected inputs before aborting
fuzz.showLogs	Whether to show console logs during fuzzing
fuzz.timeout	Timeout for the fuzz test
invariant.runs	Number of invariant test runs
invariant.depth	Number of calls per run to attempt to break the invariant
invariant.failOnRevert	Whether to fail the invariant if a revert occurs
invariant.callOverride	Whether to override unsafe external calls
invariant.timeout	Timeout for the invariant test
allowInternalExpectRevert	Allow expecting reverts at the same callstack depth as the test

Foundry compatibility

Hardhat also accepts the forge-config: prefix, kebab-case keys, and the default profile, so existing Foundry inline configuration works without changes:

/// forge-config: default.fuzz.runs = 10000
/// forge-config: fuzz.max-test-rejects = 500
function testTransferFuzz(uint256 amount) public {
  // ...
}