1 files changed, 125 insertions, 0 deletions
diff --git a/tst/metrics_trace.test.ts b/tst/metrics_trace.test.ts
new file mode 100644
index 0000000..23d5147
--- /dev/null
+++ b/tst/metrics_trace.test.ts
@@ -0,0 +1,125 @@
+import { Metric, MetricsTrace, MetricValueTag, isMetricsTraceSupplier, type MetricValue } from '../lib/index';
+
+describe('trace/metric/trace (MetricsTrace)', () => {
+    beforeEach(() => {
+        jest.useFakeTimers();
+        jest.setSystemTime(new Date('2020-01-01T00:00:00.000Z'));
+    });
+
+    afterEach(() => {
+        jest.useRealTimers();
+    });
+
+    test('isMetricsTraceSupplier accepts metrics and values', () => {
+        const m = Metric.fromName('m');
+        const v = m.count.withValue(1);
+
+        expect(isMetricsTraceSupplier(m)).toBe(true);
+        expect(isMetricsTraceSupplier(v)).toBe(true);
+        expect(isMetricsTraceSupplier([m, v])).toBe(true);
+        expect(isMetricsTraceSupplier('nope')).toBe(false);
+        expect(isMetricsTraceSupplier(undefined)).toBe(false);
+    });
+
+    test('traceScope + trace ends a metric and emits count/time', () => {
+        const emitted: MetricValue[] = [];
+        const consumer = (vals: MetricValue[]) => emitted.push(...vals);
+
+        const metric = Metric.fromName('A');
+        const t0 = new MetricsTrace(consumer).traceScope(metric);
+
+        jest.setSystemTime(new Date('2020-01-01T00:00:00.100Z'));
+        t0.trace(metric);
+
+        expect(emitted).toEqual(
+            expect.arrayContaining([
+                expect.objectContaining({ _tag: MetricValueTag, name: 'A.count', value: 1 }),
+                expect.objectContaining({ _tag: MetricValueTag, name: 'A.time', value: 100 }),
+            ]),
+        );
+    });
+
+    test('trace does not emit when given string/undefined', () => {
+        const emitted: MetricValue[] = [];
+        const consumer = (vals: MetricValue[]) => emitted.push(...vals);
+        const t = new MetricsTrace(consumer);
+
+        t.trace(undefined);
+        t.trace('hello');
+        expect(emitted).toEqual([]);
+    });
+
+    test('parent-based metric emits relative to parent start', () => {
+        const emitted: MetricValue[] = [];
+        const consumer = (vals: MetricValue[]) => emitted.push(...vals);
+
+        const parent = Metric.fromName('parent');
+        const child = parent.child('child');
+
+        const t0 = new MetricsTrace(consumer).traceScope(parent);
+
+        jest.setSystemTime(new Date('2020-01-01T00:00:00.050Z'));
+        const t1 = t0.trace(child);
+
+        expect(emitted).toEqual(
+            expect.arrayContaining([
+                expect.objectContaining({ name: 'parent.child.count', value: 1 }),
+                expect.objectContaining({ name: 'parent.child.time', value: 50 }),
+            ]),
+        );
+
+        // end parent normally
+        jest.setSystemTime(new Date('2020-01-01T00:00:00.080Z'));
+        t1.trace(parent);
+        expect(emitted).toEqual(
+            expect.arrayContaining([
+                expect.objectContaining({ name: 'parent.count', value: 1 }),
+                expect.objectContaining({ name: 'parent.time', value: 80 }),
+            ]),
+        );
+
+        // child should be considered completed already
+        const before = emitted.length;
+        jest.setSystemTime(new Date('2020-01-01T00:00:00.100Z'));
+        t1.trace(child);
+        expect(emitted.length).toBe(before);
+    });
+
+    test('nested scope can end parent metric via result child', () => {
+        const emitted: MetricValue[] = [];
+        const consumer = (vals: MetricValue[]) => emitted.push(...vals);
+
+        const result = Metric.fromName('job').asResult();
+
+        const root = new MetricsTrace(consumer).traceScope(result);
+
+        jest.setSystemTime(new Date('2020-01-01T00:00:00.100Z'));
+        const child = root.traceScope('child-scope');
+        const childAfterSuccess = child.trace(result.success);
+
+        expect(emitted).toEqual(
+            expect.arrayContaining([
+                expect.objectContaining({ name: 'job.success.count', value: 1 }),
+                expect.objectContaining({ name: 'job.success.time', value: 100 }),
+            ]),
+        );
+
+        const before = emitted.length;
+        jest.setSystemTime(new Date('2020-01-01T00:00:00.200Z'));
+        childAfterSuccess.trace(result.success);
+        expect(emitted.length).toBe(before);
+    });
+
+    test('trace forwards MetricValue emissions unchanged', () => {
+        const emitted: MetricValue[] = [];
+        const consumer = (vals: MetricValue[]) => emitted.push(...vals);
+
+        const metric = Metric.fromName('X');
+        const value = metric.count.withValue(7);
+
+        const t = new MetricsTrace(consumer);
+        t.trace(value);
+
+        expect(emitted).toEqual([value]);
+    });
+});