FIX: Include sub-sub-categories in new/unread counts (#8710)

The count used to be less than the real one because the topics in
sub-sub-categories and deeper were not taken into account.

test/javascripts/models/topic-tracking-state-test.js.es6

@@ -1,6 +1,7 @@
 import TopicTrackingState from "discourse/models/topic-tracking-state";
 import createStore from "helpers/create-store";
 import Category from "discourse/models/category";
+import { NotificationLevels } from "discourse/lib/notification-levels";
 
 QUnit.module("model:topic-tracking-state");
 
@@ -91,3 +92,79 @@ QUnit.test("subscribe to category", function(assert) {
     "expect to properly track incoming for subcategory"
   );
 });
+
+QUnit.test("getSubCategoryIds", assert => {
+  const store = createStore();
+  const foo = store.createRecord("category", { id: 1, slug: "foo" });
+  const bar = store.createRecord("category", {
+    id: 2,
+    slug: "bar",
+    parent_category_id: foo.id
+  });
+  const baz = store.createRecord("category", {
+    id: 3,
+    slug: "baz",
+    parent_category_id: bar.id
+  });
+  sandbox.stub(Category, "list").returns([foo, bar, baz]);
+
+  const state = TopicTrackingState.create();
+  assert.deepEqual(Array.from(state.getSubCategoryIds(1)), [1, 2, 3]);
+  assert.deepEqual(Array.from(state.getSubCategoryIds(2)), [2, 3]);
+  assert.deepEqual(Array.from(state.getSubCategoryIds(3)), [3]);
+});
+
+QUnit.test("countNew", assert => {
+  const store = createStore();
+  const foo = store.createRecord("category", { id: 1, slug: "foo" });
+  const bar = store.createRecord("category", {
+    id: 2,
+    slug: "bar",
+    parent_category_id: foo.id
+  });
+  const baz = store.createRecord("category", {
+    id: 3,
+    slug: "baz",
+    parent_category_id: bar.id
+  });
+  sandbox.stub(Category, "list").returns([foo, bar, baz]);
+
+  const state = TopicTrackingState.create();
+
+  assert.equal(state.countNew(1), 0);
+  assert.equal(state.countNew(2), 0);
+  assert.equal(state.countNew(3), 0);
+
+  state.states["t112"] = {
+    last_read_post_number: null,
+    id: 112,
+    notification_level: NotificationLevels.TRACKING,
+    category_id: 2
+  };
+
+  assert.equal(state.countNew(1), 1);
+  assert.equal(state.countNew(2), 1);
+  assert.equal(state.countNew(3), 0);
+
+  state.states["t113"] = {
+    last_read_post_number: null,
+    id: 113,
+    notification_level: NotificationLevels.TRACKING,
+    category_id: 3
+  };
+
+  assert.equal(state.countNew(1), 2);
+  assert.equal(state.countNew(2), 2);
+  assert.equal(state.countNew(3), 1);
+
+  state.states["t111"] = {
+    last_read_post_number: null,
+    id: 111,
+    notification_level: NotificationLevels.TRACKING,
+    category_id: 1
+  };
+
+  assert.equal(state.countNew(1), 3);
+  assert.equal(state.countNew(2), 2);
+  assert.equal(state.countNew(3), 1);
+});