Inline configuration for Solidity tests

Hardhat lets you override solidity 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>.

Keys can be written in camelCase, snake_case, or kebab-case:

/// 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

By default, the expectRevert cheatcode only catches reverts from external calls, that is, calls at a lower depth than the test itself. If your test directly calls an internal function that reverts, expectRevert won’t catch it and you’ll see an error like call didn't revert at a lower depth than cheatcode call depth.

Setting allowInternalExpectRevert to true allows expectRevert to work on calls at the same depth as the test:

/// hardhat-config: allowInternalExpectRevert = true
function testInternalRevert() public {
  vm.expectRevert("some error");
  this.myInternalHelper(); // reverts at the same call depth
}

Foundry compatibility

Hardhat also accepts the forge-config: prefix 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 {
  // ...
}

Omitting the profile is equivalent to using default.