Add tests

src/components/Locale/Locale.test.ts

@@ -0,0 +1,25 @@
+import { getMatchingLocale, Locale } from "./Locale";
+
+describe("Matches locale to browser settings", () => {
+  it("if first language is an exact match", () => {
+    const locales = ["fr", "es", "en"];
+
+    expect(getMatchingLocale(locales)).toBe(Locale.FR);
+  });
+
+  it("if there is an exact match, but it's not first preference", () => {
+    const locales = ["does-not-exist", "tr", "de", "fr"];
+
+    expect(getMatchingLocale(locales)).toBe(Locale.TR);
+  });
+
+  it("or returns undefined if there is no match", () => {
+    const locales = [
+      "does-not-exist-1",
+      "does-not-exist-2",
+      "does-not-exist-3"
+    ];
+
+    expect(getMatchingLocale(locales)).toBe(undefined);
+  });
+});