We use [Codecov.io][2] here as a coverage provider for our JS tests - they're great. Unfortunately we haven't found a way to get their reports to show branch coverage for Solidity. Coveralls has excellent Solidity branch coverage reporting out of the box (see below).
Because tests run slower under coverage, it's possible to hit default mocha time limits with a test that iterates hundreds of times before producing a result. Timeouts can be disabled by configuring the mocha option in `.solcover.js` as below: (ProTip courtesy of [@cag](https://github.com/cag))
If your project is large, complex and uses ABI encoder V2 or Solidity >= V8, you may see "stack too deep" compiler errors when using solidity-coverage. This happens because:
+ solidity-coverage turns the solc optimizer off in order trace code execution correctly
+ some projects cannot compile unless the optimizer is turned on.
Work-arounds for this problem are tracked below. (These are only available in hardhat. If you're using hardhat and none of them work for you, please open an issue.)
+ Solidity's `.send` and `.transfer` methods usually work fine though.
Using `estimateGas` to calculate your gas costs or allowing your transactions to use the default gas
settings should be more resilient in most cases.
Gas metering within Solidity is increasingly seen as anti-pattern because EVM gas costs are recalibrated from fork to fork. Depending on their exact values can result in deployed contracts ceasing to behave as intended.
## Notes on branch coverage
Solidity-coverage treats `assert` and `require` as code branches because they check whether a condition is true or not. If it is, they allow execution to proceed. If not, they throw, and all changes are reverted. Indeed, prior to [Solidity 0.4.10](https://github.com/ethereum/solidity/releases/tag/v0.4.10), when `assert` and `require` were introduced, this functionality was achieved by code that looked like
Clearly, the coverage should be the same in these situations, as the code is (functionally) identical. Older versions of solidity-coverage did not treat these as branch points, and they were not considered in the branch coverage filter. Newer versions *do* count these as branch points, so if your tests did not include failure scenarios for `assert` or `require`, you may see a decrease in your coverage figures when upgrading `solidity-coverage`.
If an `assert` or `require` is marked with an `I` in the coverage report, then during your tests the conditional is never true. If it is marked with an `E`, then it is never false.
