Foundry Book

In-line test configuration

Foundry users are enabled to specify overall test configurations, using a combination of ENV variables and config statements in the foundry.toml. Checkout the Testing reference for a detailed description.

Despite this may work in the general case, some tests may need finer control over their configuration. For such reason Forge provides a way to specify per-test configs for invariant and fuzz testing scenarios.

Users can in-line test config statements directly in Solidity comments. This would affect the behavior of the forge test command for a specific test instance, as illustrated in the example below.

contract MyTest is Test {
  /// forge-config: default.fuzz.runs = 100
  /// forge-config: ci.fuzz.runs = 500
  function test_SimpleFuzzTest(uint256 x) public {
    // --- snip ---
  }
}

What we are asking here is to run our fuzzer 100 and 500 times for the default and ci profiles respectively. The interesting fact is that this would override any fuzz runs setup existing at a global level. All other configs would be inherited from the global context, making this acting as a fallback for all possible configurations.

Block comments

In-line test configurations can also be expressed in block comments, as illustrated in the example.

contract MyTest is Test {
  /**
   * forge-config: default.fuzz.runs = 1024
   * forge-config: default.fuzz.max-test-rejects = 500
   */
  function test_SimpleFuzzTest(uint256 x) public {
    // --- snip ---
  }
}

In-line fuzz configs

Users can specify the configs described in the table. Each statement must have a prefix of the form forge-config: ${PROFILE}.fuzz.

Fuzz config example

contract MyFuzzTest is Test {
  /// forge-config: default.fuzz.runs = 100
  /// forge-config: default.fuzz.max-test-rejects = 2
  function test_InlineConfig(uint256 x) public {
    // --- snip ---
  }
}

In-line invariant configs

Users can specify the configs described in the table. Each statement must have a prefix of the form forge-config: ${PROFILE}.invariant.

Invariant config example

contract MyInvariantTest is Test {
  /// forge-config: default.invariant.runs = 100
  /// forge-config: default.invariant.depth = 2
  /// forge-config: default.invariant.fail-on-revert = false
  /// forge-config: default.invariant.call-override = true
  function invariant_InlineConfig() public {
    // --- snip ---
  }
}