diff --git a/packages/time/src/tests/isValidDate.test.ts b/packages/time/src/tests/isValidDate.test.ts
index 57a3556..4d01970 100644
--- a/packages/time/src/tests/isValidDate.test.ts
+++ b/packages/time/src/tests/isValidDate.test.ts
@@ -1,16 +1,34 @@
-import {describe, expect, test} from 'vitest';
-import {isValidDate} from '../utils/isValidDate';
+import { describe, expect, test } from 'vitest'
+import { isValidDate } from '../utils/isValidDate'
 
 describe('isValidDate', () => {
   test('should return true for a valid date', () => {
-    expect(isValidDate(new Date())).toBe(true);
-  });
+    const date = new Date();
+    expect(isValidDate(date)).toBe(true)
+  })
 
-  test('should return false for an invalid date', () => {
-    expect(isValidDate(new Date("invalid"))).toBe(false);
-  });
+  test.each([
+    '2021-10-10',
+    new Date('invalid'),
+    {},
+    undefined,
+    null,
+    NaN,
+    0,
+  ])('should return false for invalid date %p', (date) => {
+    expect(isValidDate(date)).toBe(false)
+  })
 
-  test("should return false for null", () => {
-    expect(isValidDate(null)).toBe(false);
-  });
-});
\ No newline at end of file
+  test('should assert type guards correctly', () => {
+    const notADate = 'not a date';
+    if (isValidDate(notADate)) {
+      expect(notADate).toBeInstanceOf(Date)
+      notADate.getDate()
+    } else {
+      expect(() => {
+        // @ts-expect-error
+        notADate.getTime()
+      }).toThrowError()
+    }
+  })
+})
diff --git a/packages/time/src/tests/parse.test.ts b/packages/time/src/tests/parse.test.ts
index 4ee0522..d8bd6ca 100644
--- a/packages/time/src/tests/parse.test.ts
+++ b/packages/time/src/tests/parse.test.ts
@@ -1,5 +1,5 @@
-import {describe, expect, test} from 'vitest';
-import {parse} from '../utils/parse';
+import { describe, expect, test } from 'vitest'
+import { parse } from '../utils/parse'
 
 const dateTimeFormat = new Intl.DateTimeFormat('en-US', {
   year: 'numeric',
@@ -9,124 +9,136 @@ const dateTimeFormat = new Intl.DateTimeFormat('en-US', {
   minute: '2-digit',
   second: '2-digit',
   timeZoneName: 'short',
-  timeZone: 'America/New_York'
-});
+  timeZone: 'America/New_York',
+})
 
 const timeOnlyFormat = new Intl.DateTimeFormat('en-US', {
   hour: '2-digit',
   minute: '2-digit',
   second: '2-digit',
   //timeZoneName: 'short',
-  timeZone: 'America/New_York'
-});
+  timeZone: 'America/New_York',
+})
 
 describe('parse', () => {
   test('should parse a valid year only date string', () => {
-    const date = parse('2021');
-    expect(dateTimeFormat.format(date)).toBe('01/01/2021, 12:00:00 AM EST');
-  });
+    const date = parse('2021')
+    expect(dateTimeFormat.format(date)).toBe('01/01/2021, 12:00:00 AM EST')
+  })
 
   test('should parse a valid year and month only date string', () => {
-    const date = parse('2021-03');
-    expect(dateTimeFormat.format(date)).toBe('03/01/2021, 12:00:00 AM EST');
-  });
+    const date = parse('2021-03')
+    expect(dateTimeFormat.format(date)).toBe('03/01/2021, 12:00:00 AM EST')
+  })
 
   test('should parse a valid year, month and day only date string', () => {
-    const date = parse('2021-03-12');
-    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 12:00:00 AM EST');
-  });
+    const date = parse('2021-03-12')
+    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 12:00:00 AM EST')
+  })
 
   test('should cast date only string to UTC', () => {
-    const date = parse('2021-03-12TZ');
-    expect(dateTimeFormat.format(date)).toBe('03/11/2021, 07:00:00 PM EST');
-  });
+    const date = parse('2021-03-12TZ')
+    expect(dateTimeFormat.format(date)).toBe('03/11/2021, 07:00:00 PM EST')
+  })
 
   test('should cast date only string to offset', () => {
-    const date = parse('2021-03-12T-07:00');
-    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 02:00:00 AM EST');
-  });
+    const date = parse('2021-03-12T-07:00')
+    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 02:00:00 AM EST')
+  })
 
   test('should parse a valid year, month, day and hour only date/time string with separator', () => {
-    const date = parse('2021-03-12T14');
-    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 02:00:00 PM EST');
-  });
+    const date = parse('2021-03-12T14')
+    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 02:00:00 PM EST')
+  })
 
   test('should parse a valid year, month, day and hour only date/time string without separator', () => {
-    const date = parse('2021-03-12 16');
-    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 04:00:00 PM EST');
-  });
+    const date = parse('2021-03-12 16')
+    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 04:00:00 PM EST')
+  })
 
   test('should parse a valid year, month, day, hour and minute only date/time string', () => {
-    const date = parse('2021-03-12T14:42');
-    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 02:42:00 PM EST');
-  });
+    const date = parse('2021-03-12T14:42')
+    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 02:42:00 PM EST')
+  })
 
   test('should parse a valid year, month, day, hour, minute and seconds only date/time string', () => {
-    const date = parse('2021-03-12T14:42:12');
-    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 02:42:12 PM EST');
-  });
+    const date = parse('2021-03-12T14:42:12')
+    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 02:42:12 PM EST')
+  })
 
   test('should parse a valid UTC date/time string', () => {
-    const date = parse('2021-03-12T14:42:12Z');
-    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 09:42:12 AM EST');
-  });
+    const date = parse('2021-03-12T14:42:12Z')
+    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 09:42:12 AM EST')
+  })
 
   test('should parse a valid UTC date/time string with lower case separator and zulu', () => {
-    const date = parse('2021-03-12t14:42:12z');
-    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 09:42:12 AM EST');
-  });
+    const date = parse('2021-03-12t14:42:12z')
+    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 09:42:12 AM EST')
+  })
 
   test('should parse a valid date/time string with offset', () => {
-    const date = parse('2021-03-12T14:42:12+09:00');
-    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 12:42:12 AM EST');
-  });
+    const date = parse('2021-03-12T14:42:12+09:00')
+    expect(dateTimeFormat.format(date)).toBe('03/12/2021, 12:42:12 AM EST')
+  })
 
   test('should parse a valid epoch date/time', () => {
-    const date = parse(1711639239717);
-    expect(dateTimeFormat.format(date)).toBe('03/28/2024, 11:20:39 AM EDT');
-  });
+    const date = parse(1711639239717)
+    expect(dateTimeFormat.format(date)).toBe('03/28/2024, 11:20:39 AM EDT')
+  })
 
   test('should parse a valid hour and minute time string', () => {
-    const date = parse('14:00');
-    expect(timeOnlyFormat.format(date)).toBe('02:00:00 PM');
-  });
+    const date = parse('14:00')
+    expect(timeOnlyFormat.format(date)).toBe('02:00:00 PM')
+  })
 
   test('should parse a valid hour, minute and second time string', () => {
-    const date = parse('14:14:34');
-    expect(timeOnlyFormat.format(date)).toBe('02:14:34 PM');
-  });
+    const date = parse('14:14:34')
+    expect(timeOnlyFormat.format(date)).toBe('02:14:34 PM')
+  })
 
   test('should parse a valid hour, minute and second time string with meridiem', () => {
-    const date = parse('08:14:34 PM');
-    expect(timeOnlyFormat.format(date)).toBe('08:14:34 PM');
-  });
+    const date = parse('08:14:34 PM')
+    expect(timeOnlyFormat.format(date)).toBe('08:14:34 PM')
+  })
 
   test('should throw an error for an invalid date string', () => {
-    expect(() => parse('2021-15-37')).toThrowError('"2021-15-37" is an invalid RFC339 Internet Date Time string');
-  });
+    expect(() => parse('2021-15-37')).toThrowError(
+      '"2021-15-37" is an invalid RFC339 Internet Date Time string',
+    )
+  })
 
   test('should throw an error for an invalid time string', () => {
-    expect(() => parse('27:62')).toThrowError('"27:62" is an invalid RFC339 Internet Date Time string');
-  });
+    expect(() => parse('27:62')).toThrowError(
+      '"27:62" is an invalid RFC339 Internet Date Time string',
+    )
+  })
 
   test('should throw an error for an invalid time string', () => {
-    expect(() => parse('14:12 PM')).toThrowError('"14:12 PM" is an invalid time string');
-  });
+    expect(() => parse('14:12 PM')).toThrowError(
+      '"14:12 PM" is an invalid time string',
+    )
+  })
 
   test('should throw an error for an invalid epoch', () => {
-    expect(() => parse(9274309587123413)).toThrowError('"9274309587123412" is an invalid epoch date value');
-  });
-
-  /* test('should parse a valid time string', () => {
-    const date = parse('00:00:00.000Z');
-    expect(dateTimeFormat.format(date)).toBe('12/31/2020, 7:00:00 PM EST');
-  });
-
-  test('should throw an error for an invalid date string', () => {
-    expect(() => parse('2021-01-01T00:00:00.000')).toThrowError('"2021-01-01T00:00:00.000" is an invalid RFC339 Internet Date Time string');
-  });
-
-  test('should throw an error for an invalid time string', () => {
-    expect(() => parse('00:00:00.000')).toThrowError('"00:00:00.000" is an invalid time string');
-  }); */
-});
\ No newline at end of file
+    expect(() => parse(9274309587123410)).toThrowError(
+      '"9274309587123410" is an invalid epoch date value',
+    )
+  })
+
+  test.skip('should parse a valid time string', () => {
+    const date = parse('00:00:00.000Z')
+    expect(dateTimeFormat.format(date)).toBe('12/31/2020, 7:00:00 PM EST')
+  })
+
+  test.skip('should throw an error for an invalid date string', () => {
+    expect(() => parse('2021-01-01T00:00:00.000')).toThrowError(
+      '"2021-01-01T00:00:00.000" is an invalid RFC339 Internet Date Time string',
+    )
+  })
+
+  test.skip('should throw an error for an invalid time string', () => {
+    expect(() => parse('00:00:00.000')).toThrowError(
+      '"00:00:00.000" is an invalid time string',
+    )
+  })
+})
diff --git a/packages/time/src/utils/isValidDate.ts b/packages/time/src/utils/isValidDate.ts
index 987df31..c0d1599 100644
--- a/packages/time/src/utils/isValidDate.ts
+++ b/packages/time/src/utils/isValidDate.ts
@@ -4,9 +4,6 @@
  * @param date Date
  * @returns boolean
  */
-export function isValidDate(date: any): boolean {
-  if (Object.prototype.toString.call(date) !== '[object Date]') {
-    return false;
-  }
-  return date.getTime() === date.getTime();
-}
\ No newline at end of file
+export function isValidDate(date: unknown): date is Date {
+  return date instanceof Date && !isNaN(date.getTime());
+}