diff --git a/__test__/contentTypeSidebarWidget.test.ts b/__test__/contentTypeSidebarWidget.test.ts
new file mode 100644
index 0000000..058acb6
--- /dev/null
+++ b/__test__/contentTypeSidebarWidget.test.ts
@@ -0,0 +1,45 @@
+import EventEmitter from "wolfy87-eventemitter";
+
+import ContentTypeSidebarWidget from "../src/ContentTypeSidebarWidget";
+
+// Spec: wiki developer-hub/04-platform-contracts/app-sdk-reference.md
+// (ContentTypeSidebarWidget: currentContentType, getData, onSave) and the
+// published JSDoc: getData "Get the current content type data"; onSave
+// "Executes the provided callback function every time a content type is saved".
+describe("ContentTypeSidebarWidget", () => {
+    const initial = { uid: "blog", title: "Blog" } as any;
+    let emitter: EventEmitter;
+    let widget: ContentTypeSidebarWidget;
+
+    beforeEach(() => {
+        emitter = new EventEmitter();
+        widget = new ContentTypeSidebarWidget(
+            { currentContentType: initial } as any,
+            {} as any,
+            emitter
+        );
+    });
+
+    it("getData returns the content type the host sent at init", () => {
+        expect(widget.getData()).toEqual({ uid: "blog", title: "Blog" });
+        expect(widget.currentContentType).toEqual(initial);
+    });
+
+    it("getData returns the saved content type after a save", () => {
+        const saved = { uid: "blog", title: "Blog v2" };
+        emitter.emitEvent("contentTypeSave", [{ data: saved }]);
+        expect(widget.getData()).toEqual(saved);
+    });
+
+    it("onSave runs the callback on every save with the saved content type", () => {
+        const callback = jest.fn();
+        widget.onSave(callback);
+
+        emitter.emitEvent("contentTypeSave", [{ data: { uid: "a" } }]);
+        emitter.emitEvent("contentTypeSave", [{ data: { uid: "b" } }]);
+
+        expect(callback).toHaveBeenCalledTimes(2);
+        expect(callback).toHaveBeenNthCalledWith(1, { uid: "a" });
+        expect(callback).toHaveBeenNthCalledWith(2, { uid: "b" });
+    });
+});