Assertion functions — the foundation

What an assertion is

An assertion is a function that throws if its condition is false. That's it. Every test framework — node:test, Vitest, Jest — is built on top of this two-line primitive.

function assert(cond, msg) {
  if (!cond) throw new Error("assertion failed: " + (msg || "no message"));
}

assert(1 + 1 === 2, "math still works"); // passes silently
assert(1 + 1 === 3, "math broke");       // throws

Why this is the right starting point

• No magic. You can implement it yourself in 30 seconds.
• Composes with try/catch — a test that doesn't throw is a passing test.
• Stack trace points at the assertion line, not the helper.

assertEqual

A common shortcut for equality checks — same idea, better failure message:

function assertEqual(actual, expected, msg) {
  if (actual !== expected) {
    throw new Error(\`${msg || "values differ"}: got ${actual}, expected ${expected}\`);
  }
}

This is the entire skeleton. C8-02 makes the failure message useful for objects.