diff --git a/helper_test.go b/helper_test.go
new file mode 100644
index 0000000..5148d77
--- /dev/null
+++ b/helper_test.go
@@ -0,0 +1,17 @@
+package analysisutil_test
+
+import (
+	"testing"
+
+	"golang.org/x/tools/go/analysis/analysistest"
+)
+
+func WriteFiles(t *testing.T, filemap map[string]string) string {
+	t.Helper()
+	dir, clean, err := analysistest.WriteFiles(filemap)
+	if err != nil {
+		t.Fatal("unexpected error:", err)
+	}
+	t.Cleanup(clean)
+	return dir
+}
diff --git a/testdata/src/objectof/main.go b/testdata/src/objectof/main.go
deleted file mode 100644
index 408aa3d..0000000
--- a/testdata/src/objectof/main.go
+++ /dev/null
@@ -1,15 +0,0 @@
-package objectof
-
-import (
-	"fmt"
-	"io"
-	"vendored"
-)
-
-type A int
-var EOF = io.EOF
-var _ = vendored.EOF
-
-func main() {
-	fmt.Println(EOF)
-}
diff --git a/testdata/src/objectof/vendor/vendored/vendored.go b/testdata/src/objectof/vendor/vendored/vendored.go
deleted file mode 100644
index c965bf3..0000000
--- a/testdata/src/objectof/vendor/vendored/vendored.go
+++ /dev/null
@@ -1,5 +0,0 @@
-package vendored
-
-import "io"
-
-var EOF = io.EOF
diff --git a/types.go b/types.go
index 4773ac4..46b9706 100644
--- a/types.go
+++ b/types.go
@@ -196,3 +196,13 @@ func mergeTypesInfo(i1, i2 *types.Info) {
 	// InitOrder
 	i1.InitOrder = append(i1.InitOrder, i2.InitOrder...)
 }
+
+// Under returns the most bottom underlying type.
+func Under(t types.Type) types.Type {
+	switch t := t.(type) {
+	case *types.Named:
+		return Under(t.Underlying())
+	default:
+		return t
+	}
+}
diff --git a/types_test.go b/types_test.go
index 6b44660..a539c33 100644
--- a/types_test.go
+++ b/types_test.go
@@ -1,57 +1,117 @@
 package analysisutil_test
 
 import (
+	"errors"
+	"fmt"
 	"go/token"
+	"go/types"
+	"path/filepath"
 	"testing"
 
 	"github.com/gostaticanalysis/analysisutil"
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/analysistest"
-	"golang.org/x/tools/go/analysis/passes/buildssa"
 )
 
-const pkg = "objectof"
+func TestObjectOf(t *testing.T) {
+	t.Parallel()
 
-var typesAnalyzer = &analysis.Analyzer{
-	Name: "test_types",
-	Run:  run_test_types,
-	Requires: []*analysis.Analyzer{
-		buildssa.Analyzer,
-	},
-}
-
-func Test_Types(t *testing.T) {
-	testdata := analysistest.TestData()
-	analysistest.Run(t, testdata, typesAnalyzer, pkg)
-}
-
-func run_test_types(pass *analysis.Pass) (interface{}, error) {
-	tests := []struct {
-		path, name string
-		found      bool
+	cases := map[string]struct {
+		src   string
+		pkg   string // blank means same as the map key
+		name  string
+		found bool
 	}{
-		{"fmt", "Println", true},
-		{pkg, "A", true},
-		{pkg, "EOF", true},
-		{"io", "EOF", true},
-		{"reflect", "Kind", false},
-		{"a", "ok", false},
-		{"vendored", "EOF", true},
-		{"c", "EOF", false},
-		{"database/sql", "*DB", false},
+		"standard":    {`import _ "fmt"`, "fmt", "Println", true},
+		"unimport":    {"", "fmt", "Println", false},
+		"notexiststd": {`import _ "fmt"`, "fmt", "NOTEXIST", false},
+		"typename":    {"type A int", "", "A", true},
+		"unexportvar": {"var n int", "", "n", true},
+		"exportvar":   {"var N int", "", "N", true},
+		"notexist":    {"", "", "NOTEXIST", false},
+		"vendored":    {`import _ "fmt"`, "vendor/fmt", "Println", true},
+		"pointer":     {"type A int", "", "*A", false},
 	}
 
-	for _, tt := range tests {
-		tt := tt
-		obj := analysisutil.ObjectOf(pass, tt.path, tt.name)
+	for name, tt := range cases {
+		name, tt := name, tt
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			a := &analysis.Analyzer{
+				Name: name + "Analyzer",
+				Run: func(pass *analysis.Pass) (interface{}, error) {
+					pkg := name
+					if tt.pkg != "" {
+						pkg = tt.pkg
+					}
+					obj := analysisutil.ObjectOf(pass, pkg, tt.name)
+					switch {
+					case tt.found && obj == nil:
+						return nil, errors.New("expect found but not found")
+					case !tt.found && obj != nil:
+						return nil, fmt.Errorf("unexpected return value: %v", obj)
+					}
+					return nil, nil
+				},
+			}
+			path := filepath.Join(name, name+".go")
+			dir := WriteFiles(t, map[string]string{
+				path: fmt.Sprintf("package %s\n%s", name, tt.src),
+			})
+			analysistest.Run(t, dir, a, name)
+		})
+	}
 
-		if obj == nil && tt.found {
-			pass.Reportf(token.NoPos, "objectof could not find %s.%s", tt.path, tt.name)
-		}
-		if obj != nil && !tt.found {
-			pass.Reportf(token.NoPos, "objectof found %s.%s, which does not exist", tt.path, tt.name)
+}
+
+func TestUnder(t *testing.T) {
+	t.Parallel()
+
+	lookup := func(pass *analysis.Pass, n string) (types.Type, error) {
+		_, obj := pass.Pkg.Scope().LookupParent(n, token.NoPos)
+		if obj == nil {
+			return nil, fmt.Errorf("does not find: %s", n)
 		}
+		return obj.Type(), nil
+	}
+
+	cases := map[string]struct {
+		src  string
+		typ  string
+		want string
+	}{
+		"nonamed":  {"", "int", "int"},
+		"named":    {"type A int", "A", "int"},
+		"twonamed": {"type A int; type B A", "B", "int"},
 	}
 
-	return nil, nil
+	for name, tt := range cases {
+		name, tt := name, tt
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			a := &analysis.Analyzer{
+				Name: name + "Analyzer",
+				Run: func(pass *analysis.Pass) (interface{}, error) {
+					typ, err := lookup(pass, tt.typ)
+					if err != nil {
+						return nil, err
+					}
+					want, err := lookup(pass, tt.want)
+					if err != nil {
+						return nil, err
+					}
+					got := analysisutil.Under(typ)
+					if !types.Identical(want, got) {
+						return nil, fmt.Errorf("want %v but got %v", want, got)
+					}
+					return nil, nil
+				},
+			}
+			path := filepath.Join(name, name+".go")
+			dir := WriteFiles(t, map[string]string{
+				path: fmt.Sprintf("package %s\n%s", name, tt.src),
+			})
+			analysistest.Run(t, dir, a, name)
+		})
+	}
 }