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benchmarks/harness/tests/streak-tracker.test.ts

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+/**
+ * Task 2.5 Stage 1.5 §7.2 — StreakTracker tests.
+ *
+ * Verifies the consecutive-fetch-transport-failure counter, reset semantics,
+ * and observability surface (getRecentWindow, summary).
+ */
+
+import { describe, expect, it } from 'vitest';
+import { StreakTracker, isFetchTransportFailure } from '../src/streak-tracker.js';
+
+describe('isFetchTransportFailure', () => {
+  it('matches fetch_error_* patterns', () => {
+    expect(isFetchTransportFailure('fetch_error_TypeError')).toBe(true);
+    expect(isFetchTransportFailure('fetch_error_RangeError')).toBe(true);
+    expect(isFetchTransportFailure('fetch_error_SyntaxError')).toBe(true);
+  });
+
+  it('does NOT match non-fetch patterns', () => {
+    expect(isFetchTransportFailure(null)).toBe(false);
+    expect(isFetchTransportFailure(undefined)).toBe(false);
+    expect(isFetchTransportFailure('timeout')).toBe(false);
+    expect(isFetchTransportFailure('http_500')).toBe(false);
+    expect(isFetchTransportFailure('http_404')).toBe(false);
+    expect(isFetchTransportFailure('')).toBe(false);
+    expect(isFetchTransportFailure('FETCH_ERROR_TypeError')).toBe(false); // case-sensitive
+  });
+});
+
+describe('StreakTracker — halt trigger', () => {
+  it('does not halt on 4 consecutive fetch_error_TypeError', () => {
+    const t = new StreakTracker();
+    for (let i = 0; i < 4; i++) {
+      expect(t.record('fetch_error_TypeError')).toBe(false);
+    }
+    expect(t.getConsecutiveFailures()).toBe(4);
+  });
+
+  it('halts on the 5th consecutive fetch_error_TypeError', () => {
+    const t = new StreakTracker();
+    for (let i = 0; i < 4; i++) t.record('fetch_error_TypeError');
+    expect(t.record('fetch_error_TypeError')).toBe(true);
+    expect(t.getConsecutiveFailures()).toBe(5);
+  });
+
+  it('resets counter on a successful call (null failureMode)', () => {
+    const t = new StreakTracker();
+    for (let i = 0; i < 4; i++) t.record('fetch_error_TypeError');
+    t.record(null);
+    expect(t.getConsecutiveFailures()).toBe(0);
+    for (let i = 0; i < 4; i++) {
+      expect(t.record('fetch_error_TypeError')).toBe(false);
+    }
+  });
+
+  it('resets counter on timeout (AbortError)', () => {
+    const t = new StreakTracker();
+    t.record('fetch_error_TypeError');
+    t.record('fetch_error_TypeError');
+    t.record('timeout');
+    expect(t.getConsecutiveFailures()).toBe(0);
+  });
+
+  it('resets counter on http_5xx', () => {
+    const t = new StreakTracker();
+    t.record('fetch_error_TypeError');
+    t.record('fetch_error_TypeError');
+    t.record('http_502');
+    expect(t.getConsecutiveFailures()).toBe(0);
+  });
+
+  it('mixes fetch_error_* subtypes and counts them all', () => {
+    const t = new StreakTracker();
+    t.record('fetch_error_TypeError');
+    t.record('fetch_error_RangeError');
+    t.record('fetch_error_TypeError');
+    t.record('fetch_error_SyntaxError');
+    expect(t.record('fetch_error_TypeError')).toBe(true); // 5th consecutive
+  });
+});
+
+describe('StreakTracker — configuration', () => {
+  it('honours a custom threshold', () => {
+    const t = new StreakTracker({ threshold: 3 });
+    t.record('fetch_error_TypeError');
+    t.record('fetch_error_TypeError');
+    expect(t.record('fetch_error_TypeError')).toBe(true);
+  });
+
+  it('clamps threshold to minimum of 1', () => {
+    const t = new StreakTracker({ threshold: 0 });
+    expect(t.record('fetch_error_TypeError')).toBe(true); // threshold clamped to 1
+  });
+
+  it('honours a custom window size', () => {
+    const t = new StreakTracker({ windowSize: 3 });
+    t.record('fetch_error_TypeError');
+    t.record(null);
+    t.record('fetch_error_TypeError');
+    t.record(null); // oldest entry slides out
+    const w = t.getRecentWindow();
+    expect(w).toHaveLength(3);
+  });
+});
+
+describe('StreakTracker — observability', () => {
+  it('getRecentWindow returns snapshot of last N outcomes', () => {
+    const t = new StreakTracker({ windowSize: 5 });
+    t.record('fetch_error_TypeError');
+    t.record(null);
+    t.record('fetch_error_TypeError');
+    t.record('timeout');
+    t.record('fetch_error_TypeError');
+    expect(t.getRecentWindow()).toEqual([true, false, true, false, true]);
+  });
+
+  it('caps window at windowSize', () => {
+    const t = new StreakTracker({ windowSize: 3 });
+    for (let i = 0; i < 7; i++) {
+      t.record(i % 2 === 0 ? 'fetch_error_TypeError' : null);
+    }
+    expect(t.getRecentWindow()).toHaveLength(3);
+  });
+
+  it('summary() returns a human-readable status line', () => {
+    const t = new StreakTracker({ threshold: 5, windowSize: 5 });
+    t.record('fetch_error_TypeError');
+    t.record('fetch_error_TypeError');
+    t.record(null);
+    const s = t.summary();
+    expect(s).toContain('consecutive=0');
+    expect(s).toContain('threshold=5');
+    expect(s).toContain('[XX.]');
+  });
+});
+
+describe('StreakTracker — reset', () => {
+  it('reset clears both counter and window', () => {
+    const t = new StreakTracker();
+    t.record('fetch_error_TypeError');
+    t.record('fetch_error_TypeError');
+    t.reset();
+    expect(t.getConsecutiveFailures()).toBe(0);
+    expect(t.getRecentWindow()).toEqual([]);
+  });
+});