test: Fix flakiness in group_delete_test.go (#6624)

The test and utility were assuming that node 1 was in group 1, node 2 in
group 2, and so on. This is not true all the time, hence the flakiness.

Fixing the code to not make this assumptions as well as retrying the
DropAll in NodesSetup to ensure all the nodes are up before proceeding
with the test.

systest/group-delete/group_delete_test.go

@@ -40,7 +40,16 @@ import (
 func NodesSetup(t *testing.T, c *dgo.Dgraph) {
 	ctx := context.Background()
 
-	require.NoError(t, c.Alter(ctx, &api.Operation{DropAll: true}))
+	// Retry DropAll to make sure the nodes is up and running.
+	var err error
+	for i := 0; i < 3; i ++ {
+		if err =c.Alter(ctx, &api.Operation{DropAll: true}); err != nil {
+			time.Sleep(5*time.Second)
+			continue
+		}
+		break
+	}
+	require.NoError(t, err, "error while dropping all the data")
 
 	schema, err := ioutil.ReadFile(`../data/goldendata.schema`)
 	require.NoError(t, err)
@@ -157,7 +166,10 @@ func TestNodes(t *testing.T) {
 		t.Errorf("moving tablets failed")
 	}
 
-	resp, err := http.Get("http://" + testutil.SockAddrZeroHttp + "/removeNode?group=3&id=3")
+	groupNodes, err := testutil.GetNodesInGroup("3")
+	require.NoError(t, err)
+	resp, err := http.Get("http://" + testutil.SockAddrZeroHttp + "/removeNode?group=3&id=" +
+		groupNodes[0])
 	require.NoError(t, err)
 	require.NoError(t, getError(resp.Body))
 
@@ -191,7 +203,10 @@ func TestNodes(t *testing.T) {
 		t.Errorf("moving tablets failed")
 	}
 
-	resp, err = http.Get("http://" + testutil.SockAddrZeroHttp + "/removeNode?group=2&id=2")
+	groupNodes, err = testutil.GetNodesInGroup("2")
+	require.NoError(t, err)
+	resp, err = http.Get("http://" + testutil.SockAddrZeroHttp + "/removeNode?group=2&id=" +
+		groupNodes[0])
 	require.NoError(t, err)
 	require.NoError(t, getError(resp.Body))
 

testutil/zero.go

@@ -31,17 +31,19 @@ import (
 	"google.golang.org/grpc"
 )
 
+type Member struct {
+	Addr       string `json:"addr"`
+	GroupID    int    `json:"groupId"`
+	ID         string `json:"id"`
+	LastUpdate string `json:"lastUpdate"`
+	Leader     bool   `json:"leader"`
+}
+
 // StateResponse represents the structure of the JSON object returned by calling
 // the /state endpoint in zero.
 type StateResponse struct {
 	Groups map[string]struct {
-		Members map[string]struct {
-			Addr       string `json:"addr"`
-			GroupID    int    `json:"groupId"`
-			ID         string `json:"id"`
-			LastUpdate string `json:"lastUpdate"`
-			Leader     bool   `json:"leader"`
-		} `json:"members"`
+		Members map[string]Member `json:"members"`
 		Tablets map[string]struct {
 			GroupID   int    `json:"groupId"`
 			Predicate string `json:"predicate"`
@@ -79,22 +81,27 @@ func GetState() (*StateResponse, error) {
 }
 
 // GetClientToGroup returns a dgraph client connected to an alpha in the given group.
-func GetClientToGroup(groupID string) (*dgo.Dgraph, error) {
+func GetClientToGroup(gid string) (*dgo.Dgraph, error) {
 	state, err := GetState()
 	if err != nil {
 		return nil, err
 	}
 
-	group, ok := state.Groups[groupID]
+	group, ok := state.Groups[gid]
 	if !ok {
-		return nil, errors.Errorf("group %s does not exist", groupID)
+		return nil, errors.Errorf("group %s does not exist", gid)
 	}
 
 	if len(group.Members) == 0 {
-		return nil, errors.Errorf("the group %s has no members", groupID)
+		return nil, errors.Errorf("the group %s has no members", gid)
 	}
 
-	member := group.Members["1"]
+	// Select the first member found in the iteration.
+	var member Member
+	for _, m := range group.Members {
+		member = m
+		break
+	}
 	parts := strings.Split(member.Addr, ":")
 	if len(parts) != 2 {
 		return nil, errors.Errorf("the member has an invalid address: %v", member.Addr)
@@ -114,3 +121,25 @@ func GetClientToGroup(groupID string) (*dgo.Dgraph, error) {
 	}
 	return dgo.NewDgraphClient(api.NewDgraphClient(conn)), nil
 }
+
+func GetNodesInGroup(gid string) ([]string, error) {
+	state, err := GetState()
+	if err != nil {
+		return nil, err
+	}
+
+	group, ok := state.Groups[gid]
+	if !ok {
+		return nil, errors.Errorf("group %s does not exist", gid)
+	}
+
+	if len(group.Members) == 0 {
+		return nil, errors.Errorf("the group %s has no members", gid)
+	}
+
+	nodes := make([]string, 0)
+	for id := range group.Members {
+		nodes = append(nodes, id)
+	}
+	return nodes, nil
+}