diff --git a/src/common/datetime/create_duration_data.ts b/src/common/datetime/create_duration_data.ts
index d8e717b7e3..00e56c0d4c 100644
--- a/src/common/datetime/create_duration_data.ts
+++ b/src/common/datetime/create_duration_data.ts
@@ -22,7 +22,9 @@ export const createDurationData = (
         hours: Number(parts[0]) || 0,
         minutes: Number(parts[1]) || 0,
         seconds: seconds_whole,
-        milliseconds: Math.floor((seconds - seconds_whole) * 1000),
+        milliseconds: Math.floor(
+          Number((seconds - seconds_whole).toFixed(4)) * 1000
+        ),
       };
     }
     return { seconds: duration };
diff --git a/test/common/datetime/absolute_time.test.ts b/test/common/datetime/absolute_time.test.ts
new file mode 100644
index 0000000000..318ceb99de
--- /dev/null
+++ b/test/common/datetime/absolute_time.test.ts
@@ -0,0 +1,38 @@
+import type { HassConfig } from "home-assistant-js-websocket";
+import { describe, it, expect } from "vitest";
+import { absoluteTime } from "../../../src/common/datetime/absolute_time";
+import {
+  TimeFormat,
+  TimeZone,
+  type FrontendLocaleData,
+} from "../../../src/data/translation";
+
+const locale: FrontendLocaleData = {
+  language: "en-US",
+  time_zone: TimeZone.server,
+  time_format: TimeFormat.twenty_four,
+} as any;
+const config: HassConfig = { time_zone: "UTC" } as any;
+
+describe("absoluteTime", () => {
+  it("should format time correctly for same day", () => {
+    const from = new Date();
+    from.setUTCHours(13, 23);
+    const result = absoluteTime(from, locale, config);
+    expect(result).toBe("13:23");
+  });
+
+  it("should format date correctly for same year", () => {
+    const from = new Date();
+    from.setUTCMonth(9, 20);
+    from.setUTCHours(13, 23);
+    const result = absoluteTime(from, locale, config);
+    expect(result).toBe("Oct 20, 13:23");
+  });
+
+  it("should format date with year correctly", () => {
+    const from = new Date(2024, 1, 29, 13, 23);
+    const result = absoluteTime(from, locale, config);
+    expect(result).toBe("Feb 29, 2024, 13:23");
+  });
+});
diff --git a/test/common/datetime/calc_date.test.ts b/test/common/datetime/calc_date.test.ts
new file mode 100644
index 0000000000..d223301422
--- /dev/null
+++ b/test/common/datetime/calc_date.test.ts
@@ -0,0 +1,76 @@
+import type { HassConfig } from "home-assistant-js-websocket";
+import { describe, it, expect } from "vitest";
+import { addDays } from "date-fns";
+import {
+  calcDate,
+  calcDateProperty,
+  calcDateDifferenceProperty,
+  shiftDateRange,
+} from "../../../src/common/datetime/calc_date";
+import {
+  type FrontendLocaleData,
+  TimeZone,
+} from "../../../src/data/translation";
+
+const locale: FrontendLocaleData = {
+  language: "en-US",
+  time_zone: TimeZone.local,
+} as any;
+const localeServer: FrontendLocaleData = {
+  language: "en-US",
+  time_zone: TimeZone.server,
+} as any;
+const config: HassConfig = { time_zone: "UTC" } as any;
+
+describe("calcDate", () => {
+  it("should calculate date correctly", () => {
+    const date = new Date(2024, 1, 28);
+    const result = calcDate(date, addDays, locale, config, 1);
+    expect(result).toEqual(new Date(2024, 1, 29));
+  });
+  it("should calculate date correctly with server time zone", () => {
+    const date = new Date(2024, 1, 28);
+    const result = calcDate(date, addDays, localeServer, config, 1);
+    expect(result).toEqual(new Date(2024, 1, 29));
+  });
+});
+
+describe("calcDateProperty", () => {
+  it("should calculate date property correctly", () => {
+    const date = new Date(2023, 0, 1);
+    const options = "test-options";
+    const result = calcDateProperty(
+      date,
+      (d, o) => (o === options ? d.getDate() : false),
+      locale,
+      config,
+      options
+    );
+    expect(result).toBe(1);
+  });
+});
+
+describe("calcDateDifferenceProperty", () => {
+  it("should calculate date difference property correctly", () => {
+    const startDate = new Date(2023, 0, 1);
+    const endDate = new Date(2023, 0, 2);
+    const result = calcDateDifferenceProperty(
+      endDate,
+      startDate,
+      (d, o) => d.getDate() - o.getDate(),
+      locale,
+      config
+    );
+    expect(result).toBe(1);
+  });
+});
+
+describe("shiftDateRange", () => {
+  it("should shift date range correctly", () => {
+    const startDate = new Date(2024, 0, 1);
+    const endDate = new Date(2024, 0, 31);
+    const result = shiftDateRange(startDate, endDate, true, locale, config);
+    expect(result.start).toEqual(new Date(2024, 1, 1));
+    expect(result.end).toEqual(new Date(2024, 1, 29, 23, 59, 59, 999));
+  });
+});
diff --git a/test/common/datetime/create_duration_data.test.ts b/test/common/datetime/create_duration_data.test.ts
new file mode 100644
index 0000000000..ae6f8a2aa7
--- /dev/null
+++ b/test/common/datetime/create_duration_data.test.ts
@@ -0,0 +1,45 @@
+import { describe, it, expect } from "vitest";
+import { createDurationData } from "../../../src/common/datetime/create_duration_data";
+
+describe("createDurationData", () => {
+  it("should return undefined for undefined input", () => {
+    expect(createDurationData(undefined)).toBeUndefined();
+  });
+
+  it("should parse string duration correctly", () => {
+    expect(createDurationData("1:30:15.001")).toEqual({
+      hours: 1,
+      minutes: 30,
+      seconds: 15,
+      milliseconds: 1,
+    });
+
+    expect(createDurationData("20")).toEqual({
+      seconds: 20,
+    });
+  });
+
+  it("should return undefined for invalid string duration", () => {
+    expect(createDurationData("1:30:15:20")).toBeUndefined();
+  });
+
+  it("should parse number duration correctly", () => {
+    expect(createDurationData(3600)).toEqual({ seconds: 3600 });
+  });
+
+  it("should parse object duration without days correctly", () => {
+    expect(createDurationData({ hours: 1, minutes: 30 })).toEqual({
+      hours: 1,
+      minutes: 30,
+    });
+  });
+
+  it("should handle days in object duration correctly", () => {
+    expect(createDurationData({ days: 1, hours: 1 })).toEqual({
+      hours: 25,
+      minutes: undefined,
+      seconds: undefined,
+      milliseconds: undefined,
+    });
+  });
+});
diff --git a/test/common/datetime/first_weekday.test.ts b/test/common/datetime/first_weekday.test.ts
new file mode 100644
index 0000000000..13b71d13c2
--- /dev/null
+++ b/test/common/datetime/first_weekday.test.ts
@@ -0,0 +1,42 @@
+import { describe, it, expect } from "vitest";
+import {
+  firstWeekday,
+  firstWeekdayIndex,
+} from "../../../src/common/datetime/first_weekday";
+import {
+  type FrontendLocaleData,
+  FirstWeekday,
+} from "../../../src/data/translation";
+
+const locale: FrontendLocaleData = {
+  language: "en-US",
+  first_weekday: FirstWeekday.language,
+} as any;
+const mondayLocale: FrontendLocaleData = {
+  language: "en-US",
+  first_weekday: FirstWeekday.monday,
+} as any;
+
+describe("firstWeekday", () => {
+  it("should return the correct weekday based on locale", () => {
+    expect(firstWeekday(locale)).toBe("sunday");
+  });
+
+  it("should return the correct weekday index based on locale", () => {
+    expect(firstWeekdayIndex(locale)).toBe(0);
+  });
+
+  it("should return the correct weekday when first_weekday is specified", () => {
+    expect(firstWeekday(mondayLocale)).toBe("monday");
+  });
+
+  it("should return the correct weekday index when first_weekday is specified", () => {
+    expect(firstWeekdayIndex(mondayLocale)).toBe(1);
+  });
+
+  it("should return the default weekday when first_weekday is not valid", () => {
+    expect(
+      firstWeekdayIndex({ language: "en-US", first_weekday: "invalid" } as any)
+    ).toBe(1);
+  });
+});
diff --git a/test/common/datetime/format_date.test.ts b/test/common/datetime/format_date.test.ts
index bb98f1c992..0f6339bf93 100644
--- a/test/common/datetime/format_date.test.ts
+++ b/test/common/datetime/format_date.test.ts
@@ -1,6 +1,16 @@
-import { assert, describe, it } from "vitest";
-
-import { formatDate } from "../../../src/common/datetime/format_date";
+import { describe, expect, it } from "vitest";
+import {
+  formatDate,
+  formatDateWeekdayDay,
+  formatDateShort,
+  formatDateNumeric,
+  formatDateVeryShort,
+  formatDateMonthYear,
+  formatDateMonth,
+  formatDateYear,
+  formatDateWeekday,
+  formatDateWeekdayShort,
+} from "../../../src/common/datetime/format_date";
 import {
   NumberFormat,
   TimeFormat,
@@ -13,21 +23,244 @@ import { demoConfig } from "../../../src/fake_data/demo_config";
 describe("formatDate", () => {
   const dateObj = new Date(2017, 10, 18, 11, 12, 13, 1400);
 
-  it("Formats English dates", () => {
-    assert.strictEqual(
-      formatDate(
-        dateObj,
-        {
-          language: "en",
-          number_format: NumberFormat.language,
-          time_format: TimeFormat.language,
-          date_format: DateFormat.language,
-          time_zone: TimeZone.local,
-          first_weekday: FirstWeekday.language,
-        },
-        demoConfig
-      ),
-      "November 18, 2017"
-    );
+  describe("formatDate", () => {
+    it("Formats English dates", () => {
+      expect(
+        formatDate(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("November 18, 2017");
+    });
+  });
+
+  describe("formatDateWeekdayDay", () => {
+    it("Formats weekday and day", () => {
+      expect(
+        formatDateWeekdayDay(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("Saturday, November 18");
+    });
+  });
+
+  describe("formatDateShort", () => {
+    it("Formats short date", () => {
+      expect(
+        formatDateShort(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("Nov 18, 2017");
+    });
+  });
+
+  describe("formatDateNumeric", () => {
+    it("Formats numeric date", () => {
+      expect(
+        formatDateNumeric(
+          dateObj,
+          {
+            language: "de",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("18.11.2017");
+    });
+
+    it("Formats numeric date in DMY format", () => {
+      expect(
+        formatDateNumeric(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.DMY,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("18/11/2017");
+    });
+
+    it("Formats numeric date in MDY format", () => {
+      expect(
+        formatDateNumeric(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.MDY,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("11/18/2017");
+    });
+
+    it("Formats numeric date in YMD format", () => {
+      expect(
+        formatDateNumeric(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.YMD,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("2017/11/18");
+    });
+  });
+
+  describe("formatDateVeryShort", () => {
+    it("Formats very short date", () => {
+      expect(
+        formatDateVeryShort(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("Nov 18");
+    });
+  });
+
+  describe("formatDateMonthYear", () => {
+    it("Formats month and year", () => {
+      expect(
+        formatDateMonthYear(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("November 2017");
+    });
+  });
+
+  describe("formatDateMonth", () => {
+    it("Formats month", () => {
+      expect(
+        formatDateMonth(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("November");
+    });
+  });
+
+  describe("formatDateYear", () => {
+    it("Formats year", () => {
+      expect(
+        formatDateYear(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("2017");
+    });
+  });
+
+  describe("formatDateWeekday", () => {
+    it("Formats weekday", () => {
+      expect(
+        formatDateWeekday(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("Saturday");
+    });
+  });
+
+  describe("formatDateWeekdayShort", () => {
+    it("Formats short weekday", () => {
+      expect(
+        formatDateWeekdayShort(
+          dateObj,
+          {
+            language: "en",
+            number_format: NumberFormat.language,
+            time_format: TimeFormat.language,
+            date_format: DateFormat.language,
+            time_zone: TimeZone.local,
+            first_weekday: FirstWeekday.language,
+          },
+          demoConfig
+        )
+      ).toBe("Sat");
+    });
   });
 });
diff --git a/test/common/datetime/format_date_time.test.ts b/test/common/datetime/format_date_time.test.ts
index 45508de7fa..929536de18 100644
--- a/test/common/datetime/format_date_time.test.ts
+++ b/test/common/datetime/format_date_time.test.ts
@@ -3,6 +3,7 @@ import { assert, describe, it } from "vitest";
 import {
   formatDateTime,
   formatDateTimeWithSeconds,
+  formatDateTimeNumeric,
 } from "../../../src/common/datetime/format_date_time";
 import {
   NumberFormat,
@@ -87,3 +88,40 @@ describe("formatDateTimeWithSeconds", () => {
     );
   });
 });
+
+describe("formatDateTimeNumeric", () => {
+  const dateObj = new Date(2017, 10, 18, 23, 12, 13, 400);
+
+  it("Formats English numeric date times", () => {
+    assert.strictEqual(
+      formatDateTimeNumeric(
+        dateObj,
+        {
+          language: "en",
+          number_format: NumberFormat.language,
+          time_format: TimeFormat.am_pm,
+          date_format: DateFormat.language,
+          time_zone: TimeZone.local,
+          first_weekday: FirstWeekday.language,
+        },
+        demoConfig
+      ),
+      "11/18/2017, 11:12 PM"
+    );
+    assert.strictEqual(
+      formatDateTimeNumeric(
+        dateObj,
+        {
+          language: "en",
+          number_format: NumberFormat.language,
+          time_format: TimeFormat.twenty_four,
+          date_format: DateFormat.language,
+          time_zone: TimeZone.local,
+          first_weekday: FirstWeekday.language,
+        },
+        demoConfig
+      ),
+      "11/18/2017, 23:12"
+    );
+  });
+});
diff --git a/test/common/datetime/format_duration.test.ts b/test/common/datetime/format_duration.test.ts
index c0fc46af4b..e67e8fd47c 100644
--- a/test/common/datetime/format_duration.test.ts
+++ b/test/common/datetime/format_duration.test.ts
@@ -1,6 +1,11 @@
 import "@formatjs/intl-durationformat/polyfill-force";
-import { assert, describe, it } from "vitest";
-import { formatDuration } from "../../../src/common/datetime/format_duration";
+import { expect, describe, it } from "vitest";
+import {
+  formatDuration,
+  formatDurationLong,
+  formatDurationDigital,
+  formatNumericDuration,
+} from "../../../src/common/datetime/format_duration";
 import type { FrontendLocaleData } from "../../../src/data/translation";
 import {
   DateFormat,
@@ -21,24 +26,89 @@ const LOCALE: FrontendLocaleData = {
 
 describe("formatDuration", () => {
   it("works", () => {
-    assert.strictEqual(formatDuration(LOCALE, "0.25", "min"), "0m 15s");
-    assert.strictEqual(formatDuration(LOCALE, "0.5", "min"), "0m 30s");
-    assert.strictEqual(formatDuration(LOCALE, "1", "min"), "1m");
-    assert.strictEqual(formatDuration(LOCALE, "20", "min"), "20m");
-    assert.strictEqual(formatDuration(LOCALE, "95.5", "min"), "95m 30s");
+    expect(formatDuration(LOCALE, "0.25", "min")).toBe("0m 15s");
+    expect(formatDuration(LOCALE, "0.5", "min")).toBe("0m 30s");
+    expect(formatDuration(LOCALE, "1", "min")).toBe("1m");
+    expect(formatDuration(LOCALE, "20", "min")).toBe("20m");
+    expect(formatDuration(LOCALE, "95.5", "min")).toBe("95m 30s");
 
-    assert.strictEqual(formatDuration(LOCALE, "0.25", "h"), "0h 15m");
-    assert.strictEqual(formatDuration(LOCALE, "0.5", "h"), "0h 30m");
-    assert.strictEqual(formatDuration(LOCALE, "1", "h"), "1h");
-    assert.strictEqual(formatDuration(LOCALE, "20", "h"), "20h");
-    assert.strictEqual(formatDuration(LOCALE, "95.5", "h"), "95h 30m");
+    expect(formatDuration(LOCALE, "0.25", "h")).toBe("0h 15m");
+    expect(formatDuration(LOCALE, "0.5", "h")).toBe("0h 30m");
+    expect(formatDuration(LOCALE, "1", "h")).toBe("1h");
+    expect(formatDuration(LOCALE, "20", "h")).toBe("20h");
+    expect(formatDuration(LOCALE, "95.5", "h")).toBe("95h 30m");
 
-    assert.strictEqual(formatDuration(LOCALE, "0", "d"), "0d");
-    assert.strictEqual(formatDuration(LOCALE, "0.4", "d"), "0d 9h");
-    assert.strictEqual(formatDuration(LOCALE, "1", "d"), "1d");
-    assert.strictEqual(formatDuration(LOCALE, "20", "d"), "20d");
-    assert.strictEqual(formatDuration(LOCALE, "95.5", "d"), "95d 12h");
-    assert.strictEqual(formatDuration(LOCALE, "95.75", "d", 0), "96d");
-    assert.strictEqual(formatDuration(LOCALE, "95.75", "d", 2), "95d 18h");
+    expect(formatDuration(LOCALE, "0", "d")).toBe("0d");
+    expect(formatDuration(LOCALE, "0.4", "d")).toBe("0d 9h");
+    expect(formatDuration(LOCALE, "1", "d")).toBe("1d");
+    expect(formatDuration(LOCALE, "20", "d")).toBe("20d");
+    expect(formatDuration(LOCALE, "95.5", "d")).toBe("95d 12h");
+    expect(formatDuration(LOCALE, "95.75", "d", 0)).toBe("96d");
+    expect(formatDuration(LOCALE, "95.75", "d", 2)).toBe("95d 18h");
+  });
+
+  it("throws error for invalid duration unit", () => {
+    expect(() => formatDuration(LOCALE, "1", "invalid_unit" as any)).toThrow(
+      "Invalid duration unit"
+    );
+  });
+});
+
+describe("formatDurationLong", () => {
+  it("formats long duration", () => {
+    const duration = { days: 1, hours: 2, minutes: 3, seconds: 4 };
+    expect(formatDurationLong(LOCALE, duration)).toBe(
+      "1 day, 2 hours, 3 minutes, 4 seconds"
+    );
+  });
+});
+
+describe("formatDurationDigital", () => {
+  it("formats digital duration", () => {
+    const duration = { hours: 1, minutes: 2, seconds: 3 };
+    expect(formatDurationDigital(LOCALE, duration)).toBe("1:02:03");
+  });
+});
+
+describe("formatNumericDuration", () => {
+  it("formats numeric duration", () => {
+    const duration = { days: 1, hours: 2, minutes: 3, seconds: 4 };
+    expect(formatNumericDuration(LOCALE, duration)).toBe("1 day 2:03:04");
+  });
+
+  it("formats duration with only days", () => {
+    const duration = { days: 1 };
+    expect(formatNumericDuration(LOCALE, duration)).toBe("1 day 0:00:00");
+  });
+
+  it("formats duration with only hours", () => {
+    const duration = { hours: 1 };
+    expect(formatNumericDuration(LOCALE, duration)).toBe("1:00:00");
+  });
+
+  it("formats duration with only minutes", () => {
+    const duration = { minutes: 1 };
+    expect(formatNumericDuration(LOCALE, duration)).toBe("1:00");
+  });
+
+  it("formats duration with only seconds", () => {
+    const duration = { seconds: 1 };
+    expect(formatNumericDuration(LOCALE, duration)).toBe("1 second");
+  });
+
+  it("formats duration with only milliseconds", () => {
+    const duration = { milliseconds: 1 };
+    expect(formatNumericDuration(LOCALE, duration)).toBe("1 millisecond");
+  });
+
+  it("should not format duration with 0", () => {
+    const duration = {
+      days: 0,
+      hours: 0,
+      minutes: 0,
+      seconds: 0,
+      milliseconds: 0,
+    };
+    expect(formatNumericDuration(LOCALE, duration)).toBe(null);
   });
 });
diff --git a/test/common/datetime/format_time.test.ts b/test/common/datetime/format_time.test.ts
index 214a7eccbb..b37c8ab8b9 100644
--- a/test/common/datetime/format_time.test.ts
+++ b/test/common/datetime/format_time.test.ts
@@ -1,9 +1,10 @@
-import { assert, describe, it } from "vitest";
+import { expect, describe, it } from "vitest";
 
 import {
   formatTime,
   formatTimeWithSeconds,
   formatTimeWeekday,
+  formatTime24h,
 } from "../../../src/common/datetime/format_time";
 import {
   NumberFormat,
@@ -18,7 +19,7 @@ describe("formatTime", () => {
   const dateObj = new Date(2017, 10, 18, 23, 12, 13, 1400);
 
   it("Formats English times", () => {
-    assert.strictEqual(
+    expect(
       formatTime(
         dateObj,
         {
@@ -30,10 +31,9 @@ describe("formatTime", () => {
           first_weekday: FirstWeekday.language,
         },
         demoConfig
-      ),
-      "11:12 PM"
-    );
-    assert.strictEqual(
+      )
+    ).toBe("11:12 PM");
+    expect(
       formatTime(
         dateObj,
         {
@@ -45,9 +45,8 @@ describe("formatTime", () => {
           first_weekday: FirstWeekday.language,
         },
         demoConfig
-      ),
-      "23:12"
-    );
+      )
+    ).toBe("23:12");
   });
 });
 
@@ -55,7 +54,7 @@ describe("formatTimeWithSeconds", () => {
   const dateObj = new Date(2017, 10, 18, 23, 12, 13, 400);
 
   it("Formats English times with seconds", () => {
-    assert.strictEqual(
+    expect(
       formatTimeWithSeconds(
         dateObj,
         {
@@ -67,10 +66,9 @@ describe("formatTimeWithSeconds", () => {
           first_weekday: FirstWeekday.language,
         },
         demoConfig
-      ),
-      "11:12:13 PM"
-    );
-    assert.strictEqual(
+      )
+    ).toBe("11:12:13 PM");
+    expect(
       formatTimeWithSeconds(
         dateObj,
         {
@@ -82,9 +80,8 @@ describe("formatTimeWithSeconds", () => {
           first_weekday: FirstWeekday.language,
         },
         demoConfig
-      ),
-      "23:12:13"
-    );
+      )
+    ).toBe("23:12:13");
   });
 });
 
@@ -92,7 +89,7 @@ describe("formatTimeWeekday", () => {
   const dateObj = new Date(2017, 10, 18, 23, 12, 13, 1400);
 
   it("Formats English times", () => {
-    assert.strictEqual(
+    expect(
       formatTimeWeekday(
         dateObj,
         {
@@ -104,10 +101,9 @@ describe("formatTimeWeekday", () => {
           first_weekday: FirstWeekday.language,
         },
         demoConfig
-      ),
-      "Saturday 11:12 PM"
-    );
-    assert.strictEqual(
+      )
+    ).toBe("Saturday 11:12 PM");
+    expect(
       formatTimeWeekday(
         dateObj,
         {
@@ -119,8 +115,28 @@ describe("formatTimeWeekday", () => {
           first_weekday: FirstWeekday.language,
         },
         demoConfig
-      ),
-      "Saturday 23:12"
-    );
+      )
+    ).toBe("Saturday 23:12");
+  });
+});
+
+describe("formatTime24h", () => {
+  const dateObj = new Date(2017, 10, 18, 23, 12, 13, 1400);
+
+  it("Formats English times in 24h format", () => {
+    expect(
+      formatTime24h(
+        dateObj,
+        {
+          language: "en",
+          number_format: NumberFormat.language,
+          time_format: TimeFormat.twenty_four,
+          date_format: DateFormat.language,
+          time_zone: TimeZone.local,
+          first_weekday: FirstWeekday.language,
+        },
+        demoConfig
+      )
+    ).toBe("23:12");
   });
 });
diff --git a/test/common/datetime/localize_date.test.ts b/test/common/datetime/localize_date.test.ts
new file mode 100644
index 0000000000..61d527c616
--- /dev/null
+++ b/test/common/datetime/localize_date.test.ts
@@ -0,0 +1,65 @@
+import { describe, it, expect } from "vitest";
+import {
+  localizeWeekdays,
+  localizeMonths,
+} from "../../../src/common/datetime/localize_date";
+
+describe("localizeWeekdays", () => {
+  it("should return long weekday names in English", () => {
+    const weekdays = localizeWeekdays("en-US", false);
+    expect(weekdays).toEqual([
+      "Sunday",
+      "Monday",
+      "Tuesday",
+      "Wednesday",
+      "Thursday",
+      "Friday",
+      "Saturday",
+    ]);
+  });
+
+  it("should return short weekday names in English", () => {
+    const weekdays = localizeWeekdays("en-US", true);
+    expect(weekdays).toEqual(["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]);
+  });
+
+  // Add more tests for different languages if needed
+});
+
+describe("localizeMonths", () => {
+  it("should return long month names in English", () => {
+    const months = localizeMonths("en-US", false);
+    expect(months).toEqual([
+      "January",
+      "February",
+      "March",
+      "April",
+      "May",
+      "June",
+      "July",
+      "August",
+      "September",
+      "October",
+      "November",
+      "December",
+    ]);
+  });
+
+  it("should return short month names in English", () => {
+    const months = localizeMonths("en-US", true);
+    expect(months).toEqual([
+      "Jan",
+      "Feb",
+      "Mar",
+      "Apr",
+      "May",
+      "Jun",
+      "Jul",
+      "Aug",
+      "Sep",
+      "Oct",
+      "Nov",
+      "Dec",
+    ]);
+  });
+});
diff --git a/test/common/datetime/seconds_to_duration.test.ts b/test/common/datetime/seconds_to_duration.test.ts
index 8828c197d7..0969233111 100644
--- a/test/common/datetime/seconds_to_duration.test.ts
+++ b/test/common/datetime/seconds_to_duration.test.ts
@@ -9,5 +9,10 @@ describe("secondsToDuration", () => {
     assert.strictEqual(secondsToDuration(3665), "1:01:05");
     assert.strictEqual(secondsToDuration(39665), "11:01:05");
     assert.strictEqual(secondsToDuration(932093), "258:54:53");
+    assert.strictEqual(secondsToDuration(59), "59");
+    assert.strictEqual(secondsToDuration(3600), "1:00:00");
+    assert.strictEqual(secondsToDuration(3660), "1:01:00");
+    assert.strictEqual(secondsToDuration(60), "1:00");
+    assert.strictEqual(secondsToDuration(61), "1:01");
   });
 });
diff --git a/test/common/datetime/use_am_pm.test.ts b/test/common/datetime/use_am_pm.test.ts
new file mode 100644
index 0000000000..800e4a3c58
--- /dev/null
+++ b/test/common/datetime/use_am_pm.test.ts
@@ -0,0 +1,31 @@
+import { describe, it, expect } from "vitest";
+import { TimeFormat } from "../../../src/data/translation";
+import { useAmPm } from "../../../src/common/datetime/use_am_pm";
+
+describe("useAmPm", () => {
+  it("should return true for am_pm format", () => {
+    const locale = { time_format: TimeFormat.am_pm } as any;
+    expect(useAmPm(locale)).toBe(true);
+  });
+
+  it("should return false for 24_hour format", () => {
+    const locale = { time_format: TimeFormat.twenty_four } as any;
+    expect(useAmPm(locale)).toBe(false);
+  });
+
+  it("should return true for language format with 12-hour clock", () => {
+    const locale = {
+      time_format: TimeFormat.language,
+      language: "en-US",
+    } as any;
+    expect(useAmPm(locale)).toBe(true);
+  });
+
+  it("should return false for language format with 24-hour clock", () => {
+    const locale = {
+      time_format: TimeFormat.language,
+      language: "fr-FR",
+    } as any;
+    expect(useAmPm(locale)).toBe(false);
+  });
+});