const result = buildPeakErrorHours([session], "utc");

// All hours with errors should appear, sorted by error rate desc

expect(result.length).toBeGreaterThan(0);

expect(result.length).toBeLessThanOrEqual(5);

// The hours present should correspond to UTC hours 0, 1, 9, 23.

// formatHourLabel uses Date.setHours so labels depend on locale,

// but we can verify error rates and sub info.

const highestRate = result[0];

// hour 0: 5/10 = 50%, hour 23: 4/8 = 50%, hour 9: 3/15 = 20%, hour 1: 2/20 = 10%

expect(highestRate?.value).toMatch(/50\.00%/);

expect(result.map(({ value, sub }) => ({ value, sub }))).toStrictEqual([

{ value: "50.00%", sub: "5 errors · 10 msgs" },

{ value: "50.00%", sub: "4 errors · 8 msgs" },

{ value: "20.00%", sub: "3 errors · 15 msgs" },

{ value: "10.00%", sub: "2 errors · 20 msgs" },

]);

});

it("aggregates multiple quarter-hour buckets into the same hour in UTC mode", () => {

expect(result.length).toBe(1);

// Aggregated: 5 errors / 15 total = 33.33%

expect(result[0].value).toBe("33.33%");

expect(result[0].sub).toContain("5 errors");

expect(result[0].sub).toContain("15 msgs");

expect(result[0].sub).toBe("5 errors · 15 msgs");

});

it("shifts UTC quarter-hour buckets to local timezone in local mode", () => {

const result = buildPeakErrorHours([session], "local");

expect(result.length).toBe(2);

// Verify the sub info matches aggregated values

const subs = result.map((r) => r.sub);

expect(subs).toContain("3 errors · 10 msgs"); // local hour 5

expect(subs).toContain("4 errors · 20 msgs"); // local hour 15

expect(result.map(({ value, sub }) => ({ value, sub }))).toStrictEqual([

{ value: "30.00%", sub: "3 errors · 10 msgs" }, // local hour 5

{ value: "20.00%", sub: "4 errors · 20 msgs" }, // local hour 15

]);

});

it("wraps correctly for negative local timezone (UTC-8)", () => {

const result = buildPeakErrorHours([session], "local");

expect(result.length).toBe(1);

expect(result[0].value).toBe("50.00%");

expect(result[0].sub).toContain("5 errors");

expect(result[0].sub).toContain("10 msgs");

expect(result[0].sub).toBe("5 errors · 10 msgs");

});

it("wraps correctly for positive local timezone near midnight (UTC+8, late quarter)", () => {

const result = buildPeakErrorHours([session], "local");

expect(result.length).toBe(1);

expect(result[0].value).toBe("50.00%");

expect(result[0].sub).toContain("6 errors");

expect(result[0].sub).toContain("12 msgs");

expect(result[0].sub).toBe("6 errors · 12 msgs");

});

it("returns empty array when no sessions have errors", () => {

expect(result.length).toBe(5);

// Should be sorted by rate descending — highest rate first

const rates = result.map((r) => Number.parseFloat(r.value));

for (let i = 1; i < rates.length; i++) {

expect(rates[i - 1]).toBeGreaterThanOrEqual(rates[i]);

}

expect(result.map((r) => r.value)).toStrictEqual([

"16.00%",

"14.00%",

"12.00%",

"10.00%",

"8.00%",

]);

});

it("aggregates across multiple sessions", () => {

expect(result.length).toBe(1);

// quarterIndex 20 → hour 5: aggregated 10 errors / 30 msgs = 33.33%

expect(result[0].value).toBe("33.33%");

expect(result[0].sub).toContain("10 errors");

expect(result[0].sub).toContain("30 msgs");

expect(result[0].sub).toBe("10 errors · 30 msgs");

});

it("falls back to proportional allocation when utcQuarterHourMessageCounts is absent", () => {