MM-26753 Create initial sidebar categories on demand if migration hasn't ran (#14981)

* MM-26753 Change CreateInitialSidebarCategories to only take a user ID

* MM-26753 Create initial sidebar categories on demand if migration hasn't ran

* Wait for sidebar categories to be loaded in case of replication lag

app/channel_test.go

@@ -1858,3 +1858,42 @@ func TestSidebarCategory(t *testing.T) {
 		require.Equal(t, catOrder[1], createdCategory.Id, "the newly created category should be after favorites")
 	})
 }
+
+func TestGetSidebarCategories(t *testing.T) {
+	t.Run("should return the sidebar categories for the given user/team", func(t *testing.T) {
+		th := Setup(t).InitBasic()
+		defer th.TearDown()
+
+		_, err := th.App.CreateSidebarCategory(th.BasicUser.Id, th.BasicTeam.Id, &model.SidebarCategoryWithChannels{
+			SidebarCategory: model.SidebarCategory{
+				UserId:      th.BasicUser.Id,
+				TeamId:      th.BasicTeam.Id,
+				DisplayName: "new category",
+			},
+		})
+		require.Nil(t, err)
+
+		categories, err := th.App.GetSidebarCategories(th.BasicUser.Id, th.BasicTeam.Id)
+		assert.Nil(t, err)
+		assert.Len(t, categories.Categories, 4)
+	})
+
+	t.Run("should create the initial categories even if migration hasn't ran yet", func(t *testing.T) {
+		th := Setup(t).InitBasic()
+		defer th.TearDown()
+
+		// Manually add the user to the team without going through the app layer to simulate a pre-existing user/team
+		// relationship that hasn't been migrated yet
+		team := th.CreateTeam()
+		_, err := th.App.Srv().Store.Team().SaveMember(&model.TeamMember{
+			TeamId:     team.Id,
+			UserId:     th.BasicUser.Id,
+			SchemeUser: true,
+		}, 100)
+		require.Nil(t, err)
+
+		categories, err := th.App.GetSidebarCategories(th.BasicUser.Id, team.Id)
+		assert.Nil(t, err)
+		assert.Len(t, categories.Categories, 3)
+	})
+}