assert

Assert that a contract view return satisfies a comparison, on-chain.

Syntax

assert <call> [operator] [expected] [message]

Arguments

Name	Type	Description
call	expression	A :: call expression, e.g. @token(WETH)::balanceOf(@me)
[operator]	string	Comparison operator: ==, !=, >, <, >=, <=, ~=
[expected]	any	Expected value the return is compared against
[message]	string	Revert message when the assertion fails

Options

Name	Type	Description
--delta	number	Allowed delta for the ~= (approximate) operator

Examples

load assertions

# Compare a view return against a value (named method; ABI fetched automatically)
assertions:assert @token(WETH)::balanceOf(@me) >= @token.amount(WETH 10) "insufficient bal"

# Inline ABI when the return type must be explicit (no ABI lookup)
assertions:assert @token(WETH)::{balanceOf(address)(uint256) @me} >= @token.amount(WETH 10) "insufficient bal"

# Select a tuple element with a destructure lens ($ marks the element)
set $pool 0x44fA8E6f47987339850636F88629646662444217
assertions:assert $pool::{getReserves()(uint112,uint112,uint32)}[_ $ _] >= 1000 "low reserve"

# Approximate comparison with an allowed delta
set $oracle 0x0102030405060708090a0b0c0d0e0f1011121314
assertions:assert $oracle::{price()(uint256)} ~= 2000e8 --delta 50e8 "price out of range"

# Bare boolean assertion (asserts the return is true)
set $gov 0xc0dbDcA66a0636236fAbe1B3C16B1bD4C84bB1E1
assertions:assert $gov::{paused()(bool)}

Notes

• The first argument must be a :: call expression so the (contract, calldata, return type) can be captured without being evaluated off-chain.
• Inside a batch, a failed assertion reverts the whole transaction. Run standalone, the assertion is evaluated as a read-only eth_call.
• Operators map to the contract functions by return type: uint supports == != > < >= <= ~=; address/bool/bytes32 support == !=.
• Set $assertions.address to override the resolved contract (forks / testing).

See Also