chore: fix mustache type warning and add some tests (#753)

src/helpers.ts

@@ -477,22 +477,19 @@ export class Helpers {
    */
   mustache(
     str: string | undefined,
-    data: Record<
-      string,
-      string | ((substring: string, ...args: any[]) => string)
-    >
+    data: Record<string, string | Parameters<string['replace']>[1]>
   ): string {
     if (str == null) {
       return '';
     }
     for (const p in data) {
       const re = new RegExp('{{' + p + '}}', 'g');
-      str = str.replace(
-        re,
-        // TODO @Shinigami92 2022-01-14: Try to improve the type or maybe use `if`
-        // @ts-expect-error
-        data[p]
-      );
+      const value = data[p];
+      if (typeof value === 'string') {
+        str = str.replace(re, value);
+      } else {
+        str = str.replace(re, value);
+      }
     }
     return str;
   }

test/helpers.spec.ts

@@ -724,11 +724,50 @@ describe('helpers', () => {
       });
 
       describe('mustache()', () => {
-        it('returns empty string with no arguments', () => {
-          expect(
-            // @ts-expect-error
-            faker.helpers.mustache()
-          ).toBe('');
+        it('returns empty string with no template input', () => {
+          expect(faker.helpers.mustache(undefined, {})).toBe('');
+        });
+
+        it('returns empty string with empty template input', () => {
+          expect(faker.helpers.mustache('', {})).toBe('');
+        });
+
+        it('supports string replace values', () => {
+          const actual = faker.helpers.mustache('1{{value}}3', { value: '2' });
+
+          expect(actual).toBe('123');
+        });
+
+        it('supports function replace values faker values', () => {
+          const actual = faker.helpers.mustache('1{{value}}3', {
+            value: faker.datatype.string(2),
+          });
+
+          expect(actual).toHaveLength(4);
+        });
+
+        it('supports function replace values faker function', () => {
+          const actual = faker.helpers.mustache('1{{value}}3', {
+            value: () => faker.datatype.string(3),
+          });
+
+          expect(actual).toHaveLength(5);
+        });
+
+        it('supports function replace values no args', () => {
+          const actual = faker.helpers.mustache('1{{value}}3', {
+            value: () => '7',
+          });
+
+          expect(actual).toBe('173');
+        });
+
+        it('supports function replace values with args', () => {
+          const actual = faker.helpers.mustache('1{{value}}3', {
+            value: (key) => String(key.length),
+          });
+
+          expect(actual).toBe('193');
         });
       });