Complain if we detect sub-optimal ordering in distributed setup (#7576)

Fixes #6156

cmd/endpoint_test.go

@@ -17,13 +17,53 @@
 package cmd
 
 import (
+	"flag"
 	"fmt"
 	"net/url"
 	"reflect"
 	"strings"
 	"testing"
+
+	"github.com/minio/cli"
 )
 
+func TestSubOptimalEndpointInput(t *testing.T) {
+	args1 := []string{"http://localhost/d1", "http://localhost/d2", "http://localhost/d3", "http://localhost/d4"}
+	args2 := []string{"http://example.org/d1", "http://example.com/d1", "http://example.net/d1", "http://example.edu/d1"}
+
+	tests := []struct {
+		setupType SetupType
+		ctx       *cli.Context
+		endpoints EndpointList
+		isErr     bool
+	}{
+		{
+			setupType: DistXLSetupType,
+			ctx:       cli.NewContext(cli.NewApp(), flag.NewFlagSet("", flag.ContinueOnError), nil),
+			endpoints: mustGetNewEndpointList(args1...),
+			isErr:     false,
+		},
+		{
+			setupType: DistXLSetupType,
+			ctx:       cli.NewContext(cli.NewApp(), flag.NewFlagSet("", flag.ContinueOnError), nil),
+			endpoints: mustGetNewEndpointList(args2...),
+			isErr:     false,
+		},
+	}
+	for i, test := range tests {
+		test := test
+		t.Run(fmt.Sprintf("Test%d", i+1), func(t *testing.T) {
+			err := checkEndpointsSubOptimal(test.ctx, test.setupType, test.endpoints)
+			if test.isErr && err == nil {
+				t.Error("expected err but found nil")
+			}
+			if !test.isErr && err != nil {
+				t.Errorf("expected err nil but found an err %s", err)
+			}
+		})
+	}
+}
+
 func TestNewEndpoint(t *testing.T) {
 	u1, _ := url.Parse("http://localhost/path")
 	u2, _ := url.Parse("https://example.org/path")