factor out test helpers (#2093)

src/tests/helpers/api.ts

@@ -0,0 +1,32 @@
+import { ExcalidrawElement } from "../../element/types";
+
+const { h } = window;
+
+export class API {
+  static getSelectedElements = (): ExcalidrawElement[] => {
+    return h.elements.filter(
+      (element) => h.state.selectedElementIds[element.id],
+    );
+  };
+
+  static getSelectedElement = (): ExcalidrawElement => {
+    const selectedElements = API.getSelectedElements();
+    if (selectedElements.length !== 1) {
+      throw new Error(
+        `expected 1 selected element; got ${selectedElements.length}`,
+      );
+    }
+    return selectedElements[0];
+  };
+
+  static getStateHistory = () => {
+    // @ts-ignore
+    return h.history.stateHistory;
+  };
+
+  static clearSelection = () => {
+    // @ts-ignore
+    h.app.clearSelection(null);
+    expect(API.getSelectedElements().length).toBe(0);
+  };
+}