diff --git a/gopmod/gopmod_test.go b/gopmod/gopmod_test.go
new file mode 100644
index 0000000..4319a7a
--- /dev/null
+++ b/gopmod/gopmod_test.go
@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package gopmod
+
+import (
+	"log"
+	"runtime"
+	"testing"
+
+	"github.com/goplus/mod/modload/modtest"
+)
+
+func TestLookup(t *testing.T) {
+	mod := New(modtest.GopClass(t))
+	if modv, ok := mod.LookupDepMod("github.com/qiniu/x"); !ok || modv.Version != "v1.13.2" {
+		t.Fatal("mod.LookupDepMod:", modv)
+	}
+	if pkg, err := mod.Lookup("fmt"); err != nil || pkg.ModPath != "" || pkg.ModDir != runtime.GOROOT()+"/src" {
+		t.Fatal("mod.Lookup fmt:", pkg.ModPath, pkg.ModDir, "err:", err)
+	}
+	if pkg, err := mod.Lookup("github.com/goplus/community/foo"); err != nil || pkg.ModPath != "github.com/goplus/community" {
+		t.Fatal("mod.Lookup github.com/goplus/community/foo:", pkg.ModPath, pkg.ModDir, "err:", err)
+	}
+	if _, err := mod.Lookup("github.com/qiniu/y/mockhttp"); err == nil || err.Error() != `no required module provides package github.com/qiniu/y/mockhttp; to add it:
+	gop get github.com/qiniu/y/mockhttp` {
+		t.Fatal("mod.Lookup github.com/qiniu/y/mockhttp:", err)
+	}
+	if pkg, err := mod.Lookup("github.com/qiniu/x/mockhttp"); err != nil || pkg.ModPath != "github.com/qiniu/x" {
+		t.Fatal("mod.Lookup github.com/qiniu/x/mockhttp:", pkg.ModPath, pkg.ModDir, "err:", err)
+	}
+	defer func() {
+		if e := recover(); e == nil {
+			log.Fatal("mod.Lookup: no panic?")
+		}
+	}()
+	mod.Lookup("")
+}
+
+func TestPkgType(t *testing.T) {
+	mod := New(modtest.GopClass(t))
+	if mod.IsPkgtStandard("github.com/qiniu/x") {
+		t.Fatal("mod.IsPkgtStandard: true?")
+	}
+	if !mod.IsPkgtStandard("fmt") {
+		t.Fatal("mod.IsPkgtStandard: false?")
+	}
+	if pt := mod.PkgType(""); pt != PkgtInvalid {
+		t.Fatal("mod.PkgType:", pt)
+	}
+	if pt := mod.PkgType("./fmt"); pt != PkgtLocal {
+		t.Fatal("mod.PkgType ./fmt:", pt)
+	}
+	if pt := mod.PkgType("github.com/goplus/community/foo"); pt != PkgtModule {
+		t.Fatal("mod.PkgType github.com/goplus/community/foo:", pt)
+	}
+}
diff --git a/gopmod/module.go b/gopmod/module.go
index 88e622e..a298b87 100644
--- a/gopmod/module.go
+++ b/gopmod/module.go
@@ -21,7 +21,6 @@ import (
 	"log"
 	"path/filepath"
 	"runtime"
-	"sort"
 	"strings"
 	"syscall"
 
@@ -34,15 +33,19 @@ import (
 
 // -----------------------------------------------------------------------------
 
-type depmodInfo struct {
-	path string
-	real module.Version
-}
-
 type Module struct {
 	modload.Module
 	projects map[string]*Project // ext -> project
-	depmods  []depmodInfo
+	depmods_ map[string]module.Version
+}
+
+// DepMods returns all depended modules.
+// If a depended module path is replace to be a local path, it will be canonical to an absolute path.
+func (p *Module) DepMods() map[string]module.Version {
+	if p.depmods_ == nil {
+		p.depmods_ = p.Module.DepMods()
+	}
+	return p.depmods_
 }
 
 // PkgType specifies a package type.
@@ -119,12 +122,12 @@ func (p *Module) Lookup(pkgPath string) (pkg *Package, err error) {
 // lookupExternPkg lookups a external package from depended modules.
 // If modVer.Path is replace to be a local path, it will be canonical to an absolute path.
 func (p *Module) lookupExternPkg(pkgPath string) (pkg *Package, err error) {
-	for _, m := range p.depmods {
-		if isPkgInMod(pkgPath, m.path) {
-			if modDir, e := modcache.Path(m.real); e == nil {
-				modPath := m.path
+	for path, real := range p.DepMods() {
+		if isPkgInMod(pkgPath, path) {
+			if modDir, e := modcache.Path(real); e == nil {
+				modPath := path
 				dir := modDir + pkgPath[len(modPath):]
-				pkg = &Package{Type: PkgtExtern, Real: m.real, ModPath: modPath, ModDir: modDir, Dir: dir}
+				pkg = &Package{Type: PkgtExtern, Real: real, ModPath: modPath, ModDir: modDir, Dir: dir}
 			} else {
 				err = e
 			}
@@ -138,45 +141,15 @@ func (p *Module) lookupExternPkg(pkgPath string) (pkg *Package, err error) {
 // LookupDepMod lookups a depended module.
 // If modVer.Path is replace to be a local path, it will be canonical to an absolute path.
 func (p *Module) LookupDepMod(modPath string) (modVer module.Version, ok bool) {
-	for _, m := range p.depmods {
-		if m.path == modPath {
-			modVer, ok = m.real, true
-			break
-		}
-	}
+	deps := p.DepMods()
+	modVer, ok = deps[modPath]
 	return
 }
 
-// IsGopMod returns if this module is a Go+ module or not.
-func (p *Module) IsGopMod() bool {
-	const gopPkgPath = "github.com/goplus/gop"
-	_, file := filepath.Split(p.Modfile())
-	if file == "gop.mod" {
-		return true
-	}
-	if _, ok := p.LookupDepMod(gopPkgPath); ok {
-		return true
-	}
-	return p.Path() == gopPkgPath
-}
-
-func getDepMods(mod modload.Module) []depmodInfo {
-	depmods := mod.DepMods()
-	ret := make([]depmodInfo, 0, len(depmods))
-	for path, m := range depmods {
-		ret = append(ret, depmodInfo{path: path, real: m})
-	}
-	sort.Slice(ret, func(i, j int) bool {
-		return ret[i].path > ret[j].path
-	})
-	return ret
-}
-
 // New creates a module from a modload.Module instance.
 func New(mod modload.Module) *Module {
 	projects := make(map[string]*Project)
-	depmods := getDepMods(mod)
-	return &Module{projects: projects, depmods: depmods, Module: mod}
+	return &Module{projects: projects, Module: mod}
 }
 
 // Load loads a module from a local directory.
diff --git a/modload/modtest/modtest.go b/modload/modtest/modtest.go
index c3c74c6..ea8cde0 100644
--- a/modload/modtest/modtest.go
+++ b/modload/modtest/modtest.go
@@ -44,7 +44,7 @@ func Load(t *testing.T, gomodText, gopmodText string, errMsg string) modload.Mod
 	return mod
 }
 
-func GopClass(t *testing.T) {
+func GopClass(t *testing.T) modload.Module {
 	const gomodText = `
 module github.com/goplus/community
 
@@ -60,9 +60,10 @@ require (
 	if n := len(mod.Opt.ClassMods); n != 2 {
 		t.Fatal("len(mod.Opt.Import):", n)
 	}
+	return mod
 }
 
-func Import(t *testing.T) {
+func Import(t *testing.T) modload.Module {
 	const gomodText = `
 module github.com/goplus/yap
 
@@ -82,4 +83,5 @@ import yauth github.com/goplus/yap/ytest/auth
 	if n := len(mod.Opt.Projects); n != 2 {
 		t.Fatal("len(mod.Opt.Projects):", n)
 	}
+	return mod
 }