feat: support third party orm to interact with go-zero (#1286)

* fixes #987

* chore: fix test failure

* chore: add comments

* feat: support third party orm to interact with go-zero

* chore: refactor

zrpc/resolver/internal/directbuilder_test.go

@@ -0,0 +1,53 @@
+package internal
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/tal-tech/go-zero/core/lang"
+	"github.com/tal-tech/go-zero/core/mathx"
+	"google.golang.org/grpc/resolver"
+)
+
+func TestDirectBuilder_Build(t *testing.T) {
+	tests := []int{
+		0,
+		1,
+		2,
+		subsetSize / 2,
+		subsetSize,
+		subsetSize * 2,
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(strconv.Itoa(test), func(t *testing.T) {
+			var servers []string
+			for i := 0; i < test; i++ {
+				servers = append(servers, fmt.Sprintf("localhost:%d", i))
+			}
+			var b directBuilder
+			cc := new(mockedClientConn)
+			_, err := b.Build(resolver.Target{
+				Scheme:   DirectScheme,
+				Endpoint: strings.Join(servers, ","),
+			}, cc, resolver.BuildOptions{})
+			assert.Nil(t, err)
+			size := mathx.MinInt(test, subsetSize)
+			assert.Equal(t, size, len(cc.state.Addresses))
+			m := make(map[string]lang.PlaceholderType)
+			for _, each := range cc.state.Addresses {
+				m[each.Addr] = lang.Placeholder
+			}
+			assert.Equal(t, size, len(m))
+		})
+	}
+}
+
+func TestDirectBuilder_Scheme(t *testing.T) {
+	var b directBuilder
+	assert.Equal(t, DirectScheme, b.Scheme())
+}