How do coverage thresholds work and how should you set them?

A threshold turns coverage from a report into a gate. Jest compares the computed percentages to the configured values and exits non-zero when any metric falls short. Used well, it prevents coverage from drifting down. Used badly, it encourages tests that execute code without checking anything.

export default {
  collectCoverage: true,
  coverageThreshold: {
    global: {
      statements: 80,
      branches: 70,
      functions: 80,
      lines: 80,
    },
  },
};

Setting a sane floor

• Measure the current number first, then set the floor slightly below it
• Ratchet the threshold up as tests are added
• Use a per-directory override for legacy code, not a lower global number
• Keep the business-critical modules above the global floor
• Review threshold changes in code review like any other quality gate

Per-file thresholds can be counterproductive. A tiny utility with a single defensive branch may be perfectly tested at 80 percent while a payments module needs closer to full branch coverage. Express that priority through targeted directory thresholds and explicit tests, not through one number for everything.