renderer-spec - Add basic tests for literal and one level component

__tests__/renderer-spec.tsx

@@ -0,0 +1,39 @@
+import * as React from "react";
+import { render } from "../src/renderer";
+
+test("should render plain text", () => {
+  expect((render("abcd") as string).trim()).toBe("abcd");
+});
+
+test("should render numbers as text", () => {
+  expect((render(123) as string).trim()).toBe("123");
+});
+
+test("should render null and not fail for empty values", () => {
+  expect(render(null)).toBe(null);
+  expect(render(undefined)).toBe(null);
+  expect(render([])).toBe(null);
+});
+
+test("should render plain text with simple Function Component", () => {
+  function TestComponent() {
+    return "abcd";
+  }
+
+  // Note: Rendering string from JSX shows TS error (https://github.com/DefinitelyTyped/DefinitelyTyped/issues/20544). This is a workaround.
+  expect(
+    (render(
+      React.createElement((TestComponent as unknown) as React.FunctionComponent)
+    ) as string).trim()
+  ).toBe("abcd");
+});
+
+test("should render plain text with simple Class Component", () => {
+  class TestComponent extends React.Component {
+    render() {
+      return "abcd";
+    }
+  }
+
+  expect((render(<TestComponent />) as string).trim()).toBe("abcd");
+});