FIX: Remove social sharing icons from private contexts (#10213)

test/javascripts/lib/sharing-test.js

@@ -39,4 +39,29 @@ QUnit.test("addSharingId", assert => {
     1,
     "it adds sharing id to existing sharing settings"
   );
+
+  const privateContext = true;
+
+  Sharing.addSource({
+    id: "another-source"
+  });
+  Sharing.addSharingId("another-source");
+
+  assert.equal(
+    Sharing.activeSources(sharingSettings, privateContext).length,
+    0,
+    "it does not add a regular source to sources in a private context"
+  );
+
+  Sharing.addSource({
+    id: "a-private-friendly-source",
+    showInPrivateContext: true
+  });
+  Sharing.addSharingId("a-private-friendly-source");
+
+  assert.equal(
+    Sharing.activeSources(sharingSettings, privateContext).length,
+    1,
+    "it does not add a regular source to sources in a private context"
+  );
 });