Web3 & DApp Development Fundamentals · Lesson

Coverage and Gas Reports

Quality metrics.

Coverage and Gas Reports is a free Web3 & DApp Development Fundamentals lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Web3 & DApp Development Fundamentals learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Quality Metrics

Two metrics help judge contract quality:

Code coverage — how much of your Solidity is exercised by tests.
Gas usage — how expensive your functions are to call.

Both are available as Hardhat plugins, and the Toolbox includes the gas reporter.

What Coverage Tells You

Coverage measures the percentage of statements, branches, and functions touched by your tests.

Low coverage means untested code paths — potential hidden bugs.
100% coverage does not guarantee correctness, but gaps are red flags.

Installing Coverage

The solidity-coverage plugin instruments your contracts and reports coverage:

npm install --save-dev solidity-coverage

Then require it in your config:

require("solidity-coverage");

npm install --save-dev solidity-coverage
// in hardhat.config.js:
require("solidity-coverage");

Running Coverage

Run the coverage task to execute your tests with instrumentation:

npx hardhat coverage

It prints a table per file and writes an HTML report to coverage/ you can open in a browser.

npx hardhat coverage

Reading a Coverage Table

The report has four columns:

% Stmts — statements executed.
% Branch — if/else branches taken.
% Funcs — functions called.
% Lines — lines reached.

Branch coverage is often the hardest to fill — make sure both sides of every condition are tested.

The Gas Reporter

The hardhat-gas-reporter (in the Toolbox) prints gas costs for each function call during tests. Enable it in config:

module.exports = {
  gasReporter: {
    enabled: true,
  },
};

It outputs a table after npx hardhat test.

module.exports = {
  gasReporter: {
    enabled: true,
  },
};

Reading the Gas Table

The gas report shows, per method:

Min / Max / Avg gas across calls.
# calls — how often it ran in tests.
Deployment cost for each contract.

Functions that vary widely between min and max often have conditional logic worth examining.

Pricing in Fiat

The gas reporter can show estimated costs in real money by fetching a gas price and token price:

gasReporter: {
  enabled: true,
  currency: "USD",
  gasPrice: 30,
}

This helps you communicate the real cost of operations to stakeholders.

gasReporter: {
  enabled: true,
  currency: "USD",
  gasPrice: 30,
}

Toggling with Env Vars

Coverage and gas reporting slow tests down, so gate them behind an environment variable:

gasReporter: {
  enabled: process.env.REPORT_GAS === "true",
}

Run REPORT_GAS=true npx hardhat test only when you need the report.

gasReporter: {
  enabled: process.env.REPORT_GAS === "true",
}

Using Metrics in CI

In continuous integration you can:

Fail the build if coverage drops below a threshold.
Comment gas diffs on pull requests.

These guardrails keep quality from silently regressing as the codebase grows.

Outputting to a File

The gas reporter can write its table to a file for archiving or diffing in CI:

gasReporter: {
  enabled: true,
  outputFile: "gas-report.txt",
  noColors: true,
}

Disabling colors keeps the file readable. Coverage similarly produces a coverage/ HTML report and an lcov.info file.

gasReporter: {
  enabled: true,
  outputFile: "gas-report.txt",
  noColors: true,
}

Quick Check

Test your understanding of coverage and gas reports.

Recap

You learned to measure test and gas quality.

solidity-coverage reports statement, branch, function, and line coverage via npx hardhat coverage.
Branch coverage best reveals untested paths.
The gas reporter (in the Toolbox) prints per-method gas and deployment costs.
It can price calls in fiat and be toggled with an env var.
Enforce thresholds in CI to prevent regressions.

Frequently asked questions

Is the “Coverage and Gas Reports” lesson free?

Yes — the full text of “Coverage and Gas Reports” is free to read here on the web, and the Web3 & DApp Development Fundamentals course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Web3 & DApp Development Fundamentals course, upgrade to CoddyKit PRO.

What will I learn in “Coverage and Gas Reports”?

Quality metrics. You practise Web3 & DApp Development Fundamentals with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Web3 & DApp Development Fundamentals?

No prior experience is required. Web3 & DApp Development Fundamentals on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Coverage and Gas Reports” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Web3 & DApp Development Fundamentals lesson?

Yes. Every Web3 & DApp Development Fundamentals lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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