dashboards: add validation to delete dashboard by slug

Validates that there are only one folder/dashboard having that slug,
otherwise returns 412 Precondition Failed

pkg/api/dashboard_test.go

@@ -39,6 +39,12 @@ func TestDashboardApiEndpoint(t *testing.T) {
 		fakeDash.FolderId = 1
 		fakeDash.HasAcl = false
 
+		bus.AddHandler("test", func(query *m.GetDashboardsBySlugQuery) error {
+			dashboards := []*m.Dashboard{fakeDash}
+			query.Result = dashboards
+			return nil
+		})
+
 		var getDashboardQueries []*m.GetDashboardQuery
 
 		bus.AddHandler("test", func(query *m.GetDashboardQuery) error {
@@ -232,6 +238,12 @@ func TestDashboardApiEndpoint(t *testing.T) {
 		fakeDash.HasAcl = true
 		setting.ViewersCanEdit = false
 
+		bus.AddHandler("test", func(query *m.GetDashboardsBySlugQuery) error {
+			dashboards := []*m.Dashboard{fakeDash}
+			query.Result = dashboards
+			return nil
+		})
+
 		aclMockResp := []*m.DashboardAclInfoDTO{
 			{
 				DashboardId: 1,
@@ -671,6 +683,37 @@ func TestDashboardApiEndpoint(t *testing.T) {
 			})
 		})
 	})
+
+	Convey("Given two dashboards with the same title in different folders", t, func() {
+		dashOne := m.NewDashboard("dash")
+		dashOne.Id = 2
+		dashOne.FolderId = 1
+		dashOne.HasAcl = false
+
+		dashTwo := m.NewDashboard("dash")
+		dashTwo.Id = 4
+		dashTwo.FolderId = 3
+		dashTwo.HasAcl = false
+
+		bus.AddHandler("test", func(query *m.GetDashboardsBySlugQuery) error {
+			dashboards := []*m.Dashboard{dashOne, dashTwo}
+			query.Result = dashboards
+			return nil
+		})
+
+		role := m.ROLE_EDITOR
+
+		loggedInUserScenarioWithRole("When calling DELETE on", "DELETE", "/api/dashboards/db/dash", "/api/dashboards/db/:slug", role, func(sc *scenarioContext) {
+			CallDeleteDashboard(sc)
+
+			Convey("Should result in 412 Precondition failed", func() {
+				So(sc.resp.Code, ShouldEqual, 412)
+				result := sc.ToJson()
+				So(result.Get("status").MustString(), ShouldEqual, "multiple-slugs-exists")
+				So(result.Get("message").MustString(), ShouldEqual, m.ErrDashboardsWithSameSlugExists.Error())
+			})
+		})
+	})
 }
 
 func GetDashboardShouldReturn200(sc *scenarioContext) dtos.DashboardFullWithMeta {