add more to tests - need help though

src/plugins/data/common/field_formats/field_formats_registry.test.ts

@@ -163,4 +163,22 @@ describe('FieldFormatsRegistry', () => {
       expect(params).toHaveProperty('parsedUrl');
     });
   });
+
+  describe('setCustomParams', () => {
+    test('should provide custom setting to formatters: timezone', () => {
+      fieldFormatsRegistry = new FieldFormatsRegistry();
+      fieldFormatsRegistry.init(
+        getConfig,
+        {
+          parsedUrl: {
+            origin: '',
+            pathname: '',
+            basePath: '',
+          },
+        },
+        []
+      );
+      fieldFormatsRegistry.setCustomParams({ timezone: 'America/New_York' });
+    });
+  });
 });

src/plugins/data/server/field_formats/field_formats_service.test.ts

@@ -17,9 +17,10 @@
  * under the License.
  */
 
-import { FieldFormatsService } from './field_formats_service';
-import { DateFormat } from './converters/date_server';
 import { coreMock } from '../../../../core/server/mocks';
+import { FIELD_FORMAT_IDS } from '../../common';
+import { DateFormat } from './converters/date_server';
+import { FieldFormatsService } from './field_formats_service';
 
 describe('FieldFormatService', () => {
   test('DateFormat is server version', async () => {
@@ -32,3 +33,22 @@ describe('FieldFormatService', () => {
     expect(DateFormatFromRegsitry).toEqual(DateFormat);
   });
 });
+
+describe('DateFormat with custom timezone', () => {
+  test('should provide custom setting to formatters: timezone', async () => {
+    const service = new FieldFormatsService();
+    const fieldFormatsService = await service.start();
+    const uiSettings = coreMock.createStart().uiSettings.asScopedToClient({} as any);
+    const fieldFormatsRegistry = await fieldFormatsService.fieldFormatServiceFactory(uiSettings);
+
+    fieldFormatsRegistry.setCustomParams({ timezone: 'America/Phoenix' }); // set the timezone into the registry
+
+    const fieldFormats = fieldFormatsRegistry.getByFieldType(FIELD_FORMAT_IDS.DATE as any);
+    const DateFormatInstance = fieldFormats.find((F) => F.id === 'date');
+    expect(DateFormatInstance).toBeDefined();
+    if (DateFormatInstance) {
+      const formatter = new DateFormatInstance();
+      // how to call the formatter?
+    }
+  });
+});