Pick sensible default option for phone country dropdown (#10627)

* Pick sensible default option for phone country dropdown

* Add tests

* Add tests

test/components/views/auth/CountryDropdown-test.tsx

@@ -0,0 +1,68 @@
+/*
+Copyright 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React from "react";
+import { render } from "@testing-library/react";
+
+import CountryDropdown from "../../../../src/components/views/auth/CountryDropdown";
+import SdkConfig from "../../../../src/SdkConfig";
+
+describe("CountryDropdown", () => {
+    describe("default_country_code", () => {
+        afterEach(() => {
+            SdkConfig.unset();
+        });
+
+        it.each([
+            ["GB", 44],
+            ["IE", 353],
+            ["ES", 34],
+            ["FR", 33],
+            ["PL", 48],
+            ["DE", 49],
+        ])("should respect configured default country code for %s", (config, defaultCountryCode) => {
+            SdkConfig.add({
+                default_country_code: config,
+            });
+
+            const fn = jest.fn();
+            render(<CountryDropdown onOptionChange={fn} isSmall={false} showPrefix={false} />);
+            expect(fn).toHaveBeenCalledWith(expect.objectContaining({ prefix: defaultCountryCode.toString() }));
+        });
+    });
+
+    describe("defaultCountry", () => {
+        it.each([
+            ["en-GB", 44],
+            ["en-ie", 353],
+            ["es-ES", 34],
+            ["fr", 33],
+            ["pl", 48],
+            ["de-DE", 49],
+        ])("should pick appropriate default country for %s", (language, defaultCountryCode) => {
+            Object.defineProperty(navigator, "language", {
+                configurable: true,
+                get() {
+                    return language;
+                },
+            });
+
+            const fn = jest.fn();
+            render(<CountryDropdown onOptionChange={fn} isSmall={false} showPrefix={false} />);
+            expect(fn).toHaveBeenCalledWith(expect.objectContaining({ prefix: defaultCountryCode.toString() }));
+        });
+    });
+});