fix(replicants): set the previewScene replicant value to null when no…

…t in studio mode, instead of erroring

BREAKING CHANGE: _getPreviewScene will no longer reject when OBS is not in studio mode. It will instead set the previewScene replicant's `value` to `null`.

README.md

@@ -231,6 +231,8 @@ previewScene.on('change', newVal => {
 
 If OBS is in "Studio" mode, this Replicant's `value` will be the current scene that is in Preview.
 
+If OBS is **not** in "Studio" mode, this Replicant's `value` will be `null`.
+
 Relevant Schemas:
  - [`previewScene.json`](packages/nodecg-utility-obs/schemas/previewScene.json)
  - [`types/obs_scene.json`](packages/nodecg-utility-obs/schemas/types/obs_scene.json)

packages/nodecg-utility-obs/index.js

@@ -227,6 +227,11 @@ class OBSUtility extends OBSWebSocket {
 				sources: res.sources
 			};
 		}).catch(err => {
+			if (err.error === 'studio mode not enabled') {
+				this.replicants.previewScene.value = null;
+				return;
+			}
+
 			this.log.error('Error updating preview scene:', err);
 		});
 	}

packages/nodecg-utility-obs/test/test.js

@@ -373,6 +373,16 @@ test('#_updatePreviewScene', async t => {
 	t.deepEqual(t.context.obs.log.error.firstCall.args[1].message, 'boom');
 });
 
+test('#_updatePreviewScene sets previewScene replicant to null when not in studio mode', async t => {
+	// Tell our #setPreviewScene stub to return a promise that rejects.
+	t.context.obs.getPreviewScene.rejects({error: 'studio mode not enabled'});
+
+	await t.context.obs._updatePreviewScene();
+
+	t.true(t.context.obs.getPreviewScene.calledOnce);
+	t.is(t.context.obs.replicants.previewScene.value, null);
+});
+
 test('#_transition throws when not connected to OBS', t => { // eslint-disable-line ava/prefer-async-await
 	t.plan(1);