tests: add I18n class tests (anuraghazra#3188)

tests/i18n.test.js

@@ -0,0 +1,33 @@
+import { expect, it, describe } from "@jest/globals";
+import { I18n } from "../src/common/I18n.js";
+import { statCardLocales } from "../src/translations.js";
+
+describe("I18n", () => {
+  it("should return translated string", () => {
+    const i18n = new I18n({
+      locale: "en",
+      translations: statCardLocales({ name: "Anurag Hazra", apostrophe: "s" }),
+    });
+    expect(i18n.t("statcard.title")).toBe("Anurag Hazra's GitHub Stats");
+  });
+
+  it("should throw error if translation string not found", () => {
+    const i18n = new I18n({
+      locale: "en",
+      translations: statCardLocales({ name: "Anurag Hazra", apostrophe: "s" }),
+    });
+    expect(() => i18n.t("statcard.title1")).toThrow(
+      "statcard.title1 Translation string not found",
+    );
+  });
+
+  it("should throw error if translation not found for locale", () => {
+    const i18n = new I18n({
+      locale: "asdf",
+      translations: statCardLocales({ name: "Anurag Hazra", apostrophe: "s" }),
+    });
+    expect(() => i18n.t("statcard.title")).toThrow(
+      "'statcard.title' translation not found for locale 'asdf'",
+    );
+  });
+});