test(date): additional birthday tests

src/modules/date/index.ts

@@ -864,37 +864,34 @@ export class SimpleDateModule extends SimpleModuleBase {
       refDate?: string | Date | number;
     } = {}
   ): Date {
-    if (options.max < options.min) {
+    const { min, max, mode = 'year' } = options;
+
+    if (max < min) {
       throw new FakerError(
-        `Max ${options.max} should be larger than or equal to min ${options.min}.`
+        `Max ${max} should be larger than or equal to min ${min}.`
       );
     }
 
-    const mode = options.mode === 'age' ? 'age' : 'year';
     const refDate = toDate(options.refDate, this.faker.defaultRefDate);
     const refYear = refDate.getUTCFullYear();
 
     // If no min or max is specified, generate a random date between (now - 80) years and (now - 18) years respectively
     // So that people can still be considered as adults in most cases
 
     // Convert to epoch timestamps
-    let min: number;
-    let max: number;
+    let start: number;
+    let end: number;
     if (mode === 'age') {
-      min = new Date(refDate).setUTCFullYear(refYear - (options.max ?? 80) - 1);
-      max = new Date(refDate).setUTCFullYear(refYear - (options.min ?? 18));
+      start = new Date(refDate).setUTCFullYear(refYear - (max ?? 80) - 1);
+      end = new Date(refDate).setUTCFullYear(refYear - (min ?? 18));
     } else {
       // Avoid generating dates the first and last date of the year
       // to avoid running into other years depending on the timezone.
-      min = new Date(Date.UTC(0, 0, 2)).setUTCFullYear(
-        options.min ?? refYear - 80
-      );
-      max = new Date(Date.UTC(0, 11, 30)).setUTCFullYear(
-        options.max ?? refYear - 18
-      );
+      start = Date.UTC(min ?? refYear - 80, 0, 2);
+      end = Date.UTC(max ?? refYear - 18, 11, 30);
     }
 
-    return new Date(this.faker.number.int({ min, max }));
+    return new Date(this.faker.number.int({ min: start, max: end }));
   }
 }
 

test/modules/date.spec.ts

@@ -573,6 +573,35 @@ describe('date', () => {
           expect(birthdate).toBeInstanceOf(Date);
         });
 
+        it('returns a random birthdate that is 18+ by default', () => {
+          // Generate the latest possible value => youngest
+          faker.seed(2855577693);
+
+          const refDate = new Date();
+          const birthdate = faker.date.birthdate({ refDate });
+          expect(birthdate).toBeInstanceOf(Date);
+          const value = birthdate.valueOf();
+          const refDateValue = refDate.valueOf();
+          expect(value).toBeLessThanOrEqual(refDateValue);
+          const deltaDate = new Date(refDateValue - value);
+          expect(deltaDate.getUTCFullYear() - 1970).toBeGreaterThanOrEqual(18);
+        });
+
+        it('returns a random birthdate in one year', () => {
+          const min = 1990;
+          const max = 1990;
+
+          const birthdate = faker.date.birthdate({ min, max, mode: 'year' });
+
+          // birthdate is a date object
+          expect(birthdate).toBeInstanceOf(Date);
+          expect(birthdate.toISOString()).not.toMatch(/T00:00:00.000Z/);
+
+          // Generated date is between min and max
+          expect(birthdate.getUTCFullYear()).toBeGreaterThanOrEqual(min);
+          expect(birthdate.getUTCFullYear()).toBeLessThanOrEqual(max);
+        });
+
         it('returns a random birthdate between two years', () => {
           const min = 1990;
           const max = 2000;