Add unit test to bindReporter

src/lib/bindReporter.ts

@@ -48,7 +48,7 @@ export const bindReporter = <MetricName extends MetricType['name']>(
         // See: https://github.com/GoogleChrome/web-vitals/issues/14
         if (delta || prevValue === undefined) {
           prevValue = metric.value;
-          metric.delta = delta;
+          metric.delta = Number(delta.toFixed(2));
           metric.rating = getRating(metric.value, thresholds);
           callback(metric);
         }

test/unit/bindReporter-test.js

@@ -0,0 +1,267 @@
+import {describe, it} from 'node:test';
+import assert from 'assert';
+import {bindReporter} from '../../dist/modules/lib/bindReporter.js';
+
+describe('bindReporter', () => {
+  describe('rating classification', () => {
+    const thresholds = [0.1, 0.25]; // CLS thresholds as example
+
+    it('should return "good" for values below first threshold', () => {
+      const metric = {
+        name: 'CLS',
+        value: 0.05,
+        entries: [],
+      };
+
+      const reporter = bindReporter(() => {}, metric, thresholds, true);
+
+      reporter(true);
+      assert.equal(metric.rating, 'good');
+    });
+
+    it('should return "needs-improvement" for values between thresholds', () => {
+      const metric = {
+        name: 'CLS',
+        value: 0.15,
+        entries: [],
+      };
+
+      const reporter = bindReporter(() => {}, metric, thresholds, true);
+
+      reporter(true);
+      assert.equal(metric.rating, 'needs-improvement');
+    });
+
+    it('should return "poor" for values above second threshold', () => {
+      const metric = {
+        name: 'CLS',
+        value: 0.3,
+        entries: [],
+      };
+
+      const reporter = bindReporter(() => {}, metric, thresholds, true);
+
+      reporter(true);
+      assert.equal(metric.rating, 'poor');
+    });
+
+    it('should handle boundary values correctly', () => {
+      const metricAt1stThreshold = {
+        name: 'CLS',
+        value: 0.101,
+        entries: [],
+      };
+
+      const reporter1 = bindReporter(
+        () => {},
+        metricAt1stThreshold,
+        thresholds,
+        true,
+      );
+
+      reporter1(true);
+      assert.equal(metricAt1stThreshold.rating, 'needs-improvement');
+
+      const metricAt2ndThreshold = {
+        name: 'CLS',
+        value: 0.251,
+        entries: [],
+      };
+
+      const reporter2 = bindReporter(
+        () => {},
+        metricAt2ndThreshold,
+        thresholds,
+        true,
+      );
+
+      reporter2(true);
+      assert.equal(metricAt2ndThreshold.rating, 'poor');
+    });
+  });
+
+  describe('state management', () => {
+    it('should calculate delta correctly between reports', () => {
+      const metric = {
+        name: 'CLS',
+        value: 0.1,
+        entries: [],
+      };
+      const reports = [];
+
+      const reporter = bindReporter(
+        (m) => reports.push({...m}),
+        metric,
+        [0.1, 0.25],
+        true,
+      );
+
+      reporter(true);
+      assert.equal(reports[0].delta, 0.1);
+
+      metric.value = 0.15;
+      reporter(true);
+      assert.equal(reports[1].delta, 0.05);
+    });
+
+    describe('reportAllChanges behavior', () => {
+      it('should report all changes when reportAllChanges is true', () => {
+        const metric = {
+          name: 'CLS',
+          value: 0.1,
+          entries: [],
+        };
+        const reports = [];
+
+        const reporter = bindReporter(
+          (m) => reports.push({...m}),
+          metric,
+          [0.1, 0.25],
+          true,
+        );
+
+        reporter();
+        metric.value = 0.15;
+        reporter();
+        metric.value = 0.2;
+        reporter();
+
+        assert.equal(reports.length, 3);
+        assert.equal(reports[0].value, 0.1);
+        assert.equal(reports[1].value, 0.15);
+        assert.equal(reports[2].value, 0.2);
+      });
+
+      it('should not report when value does not change', () => {
+        const metric = {
+          name: 'CLS',
+          value: 0.1,
+          entries: [],
+        };
+        const reports = [];
+
+        const reporter = bindReporter(
+          (m) => reports.push({...m}),
+          metric,
+          [0.1, 0.25],
+          true,
+        );
+
+        reporter();
+        reporter();
+        reporter();
+
+        assert.equal(reports.length, 1);
+        assert.equal(reports[0].value, 0.1);
+      });
+
+      it('should only report on forceReport when reportAllChanges is false', () => {
+        const metric = {
+          name: 'CLS',
+          value: 0.1,
+          entries: [],
+        };
+        const reports = [];
+
+        const reporter = bindReporter(
+          (m) => reports.push({...m}),
+          metric,
+          [0.1, 0.25],
+          false,
+        );
+
+        reporter();
+        metric.value = 0.15;
+        reporter();
+        reporter(true);
+
+        assert.equal(reports.length, 1);
+        assert.equal(reports[0].value, 0.15);
+      });
+    });
+  });
+
+  describe('special values handling', () => {
+    it('should not report negative values', () => {
+      const metric = {
+        name: 'CLS',
+        value: -1,
+        entries: [],
+      };
+      const reports = [];
+
+      const reporter = bindReporter(
+        (m) => reports.push({...m}),
+        metric,
+        [0.1, 0.25],
+        true,
+      );
+
+      reporter(true);
+      assert.equal(reports.length, 0);
+    });
+
+    it('should handle zero values correctly', () => {
+      const metric = {
+        name: 'CLS',
+        value: 0,
+        entries: [],
+      };
+      const reports = [];
+
+      const reporter = bindReporter(
+        (m) => reports.push({...m}),
+        metric,
+        [0.1, 0.25],
+        true,
+      );
+
+      reporter(true);
+      assert.equal(reports.length, 1);
+      assert.equal(reports[0].value, 0);
+      assert.equal(reports[0].delta, 0);
+      assert.equal(reports[0].rating, 'good');
+    });
+
+    describe('first report behavior', () => {
+      it('should always report first value even with zero delta', () => {
+        const metric = {
+          name: 'CLS',
+          value: 0,
+          entries: [],
+        };
+        const reports = [];
+
+        const reporter = bindReporter(
+          (m) => reports.push({...m}),
+          metric,
+          [0.1, 0.25],
+          false,
+        );
+
+        reporter(true);
+        assert.equal(reports.length, 1);
+        assert.equal(reports[0].delta, 0);
+      });
+
+      it('should calculate correct delta for first non-zero value', () => {
+        const metric = {
+          name: 'CLS',
+          value: 0.1,
+          entries: [],
+        };
+        const reports = [];
+
+        const reporter = bindReporter(
+          (m) => reports.push({...m}),
+          metric,
+          [0.1, 0.25],
+          true,
+        );
+
+        reporter(true);
+        assert.equal(reports[0].delta, 0.1);
+      });
+    });
+  });
+});