retain local appState props on restore (#2224)

Co-authored-by: Lipis <lipiridis@gmail.com>

src/tests/appState.test.tsx

@@ -0,0 +1,46 @@
+import React from "react";
+import { render, waitFor } from "./test-utils";
+import App from "../components/App";
+import { API } from "./helpers/api";
+import { getDefaultAppState } from "../appState";
+
+const { h } = window;
+
+describe("appState", () => {
+  it("drag&drop file doesn't reset non-persisted appState", async () => {
+    const defaultAppState = getDefaultAppState();
+    const exportBackground = !defaultAppState.exportBackground;
+    render(
+      <App
+        initialData={{
+          appState: {
+            ...defaultAppState,
+            exportBackground,
+            viewBackgroundColor: "#F00",
+          },
+          elements: [],
+        }}
+      />,
+    );
+
+    await waitFor(() => {
+      expect(h.state.exportBackground).toBe(exportBackground);
+      expect(h.state.viewBackgroundColor).toBe("#F00");
+    });
+
+    API.dropFile({
+      appState: {
+        viewBackgroundColor: "#000",
+      },
+      elements: [API.createElement({ type: "rectangle", id: "A" })],
+    });
+
+    await waitFor(() => {
+      expect(h.elements).toEqual([expect.objectContaining({ id: "A" })]);
+      // non-imported prop → retain
+      expect(h.state.exportBackground).toBe(exportBackground);
+      // imported prop → overwrite
+      expect(h.state.viewBackgroundColor).toBe("#000");
+    });
+  });
+});