fix(viewpoints): throw a clear error when go() has no world

packages/core/src/core/Viewpoints/src/viewpoint.ts

@@ -43,7 +43,7 @@ export class Viewpoint {
     camera_up_vector: { x: 0, y: 1, z: 0 },
   };
 
-  customData: Record<string, any> = {}
+  customData: Record<string, any> = {};
 
   /**
    * A list of components GUIDs to hide when defaultVisibility = true or to show when defaultVisibility = false
@@ -346,6 +346,7 @@ export class Viewpoint {
    * @param transition - Indicates whether the camera movement should have a transition effect.
    *                      Default value is `true`.
    *
+   * @throws An error if the viewpoint has no world.
    * @throws An error if the world's camera does not have camera controls.
    *
    * @returns A Promise that resolves when the camera has been set.
@@ -356,7 +357,11 @@ export class Viewpoint {
     clippingsVisibility?: boolean;
     applyVisibility?: boolean;
   }) {
-    if (!this.world) return;
+    if (!this.world) {
+      throw new Error(
+        "Viewpoint: no world to apply the viewpoint to. Set `world` on this viewpoint, or set `Viewpoints.world` before creating or loading viewpoints (for example with `BCFTopics.load`).",
+      );
+    }
 
     const { camera } = this.world;
     if (!(camera instanceof OrthoPerspectiveCamera)) {

packages/core/src/core/Viewpoints/viewpoint-go.test.ts

@@ -0,0 +1,15 @@
+import { describe, expect, it } from "vitest";
+import { loadSourceBundle } from "../../../tests/source-bundle";
+
+// Needs the real `Components`: see `loadSourceBundle`.
+const OBC = await loadSourceBundle();
+
+describe("Viewpoint.go", () => {
+  it("rejects with a clear error when the viewpoint has no world", async () => {
+    const components = new OBC.Components();
+    const viewpoints = components.get(OBC.Viewpoints);
+    expect(viewpoints.world).toBeNull();
+    const viewpoint = viewpoints.create();
+    await expect(viewpoint.go()).rejects.toThrow(/no world/);
+  });
+});