diff --git a/internal/errors/discoverer.go b/internal/errors/discoverer.go
index ead7be84b7..c792e037be 100644
--- a/internal/errors/discoverer.go
+++ b/internal/errors/discoverer.go
@@ -18,21 +18,26 @@
 package errors
 
 var (
+	// ErrAddrCouldNotDiscover represents a function to generate an error that address couldn't discover.
 	ErrAddrCouldNotDiscover = func(err error, record string) error {
 		return Wrapf(err, "addr %s ip couldn't discover", record)
 	}
 
+	// ErrNodeNotFound represents a function to generate an error of discover node not found.
 	ErrNodeNotFound = func(node string) error {
 		return Errorf("discover node %s not found", node)
 	}
 
+	// ErrNamespaceNotFound represents a function to generate an error of discover namespace not found.
 	ErrNamespaceNotFound = func(ns string) error {
 		return Errorf("discover namespace %s not found", ns)
 	}
 
+	// ErrPodNameNotFound represents a function to generate an error of discover pod not found.
 	ErrPodNameNotFound = func(name string) error {
 		return Errorf("discover pod %s not found", name)
 	}
 
+	// ErrInvalidDiscoveryCache represents an error that type conversion of discovery cache failed.
 	ErrInvalidDiscoveryCache = New("cache type cast failed")
 )
diff --git a/internal/errors/discoverer_test.go b/internal/errors/discoverer_test.go
new file mode 100644
index 0000000000..de1ef37f86
--- /dev/null
+++ b/internal/errors/discoverer_test.go
@@ -0,0 +1,335 @@
+//
+// Copyright (C) 2019-2020 Vdaas.org Vald team ( kpango, rinx, kmrmt )
+//
+// 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
+//
+//    https://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 errors
+
+import "testing"
+
+func TestErrAddrCouldNotDiscover(t *testing.T) {
+	type args struct {
+		err    error
+		record string
+	}
+	type want struct {
+		want error
+	}
+	type test struct {
+		name       string
+		args       args
+		want       want
+		checkFunc  func(want, error) error
+		beforeFunc func(args)
+		afterFunc  func(args)
+	}
+	defaultCheckFunc := func(w want, got error) error {
+		if !Is(got, w.want) {
+			return Errorf("got: \"%#v\",\n\t\t\t\twant: \"%#v\"", got, w.want)
+		}
+		return nil
+	}
+	tests := []test{
+		{
+			name: "returns wrapped discover error when err is server error and record is '127.0.0.1'",
+			args: args{
+				err:    New("server error"),
+				record: "127.0.0.1",
+			},
+			want: want{
+				want: New("addr 127.0.0.1 ip couldn't discover: server error"),
+			},
+		},
+		{
+			name: "returns wrapped discover error when err is server error and record is empty",
+			args: args{
+				err:    New("server error"),
+				record: "",
+			},
+			want: want{
+				want: New("addr  ip couldn't discover: server error"),
+			},
+		},
+		{
+			name: "returns discover error when err is nil error and record is '127.0.0.1'",
+			args: args{
+				err:    nil,
+				record: "127.0.0.1",
+			},
+			want: want{
+				want: New("addr 127.0.0.1 ip couldn't discover"),
+			},
+		},
+		{
+			name: "returns discover error when err is nil error and record is empty",
+			args: args{
+				err:    nil,
+				record: "",
+			},
+			want: want{
+				want: New("addr  ip couldn't discover"),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(tt *testing.T) {
+			if test.beforeFunc != nil {
+				test.beforeFunc(test.args)
+			}
+			if test.afterFunc != nil {
+				defer test.afterFunc(test.args)
+			}
+			if test.checkFunc == nil {
+				test.checkFunc = defaultCheckFunc
+			}
+
+			got := ErrAddrCouldNotDiscover(test.args.err, test.args.record)
+			if err := test.checkFunc(test.want, got); err != nil {
+				tt.Errorf("error = %v", err)
+			}
+		})
+	}
+}
+
+func TestErrNodeNotFound(t *testing.T) {
+	type args struct {
+		node string
+	}
+	type want struct {
+		want error
+	}
+	type test struct {
+		name       string
+		args       args
+		want       want
+		checkFunc  func(want, error) error
+		beforeFunc func(args)
+		afterFunc  func(args)
+	}
+	defaultCheckFunc := func(w want, got error) error {
+		if !Is(got, w.want) {
+			return Errorf("got: \"%#v\",\n\t\t\t\twant: \"%#v\"", got, w.want)
+		}
+		return nil
+	}
+	tests := []test{
+		{
+			name: "returns discover node not found error when node is '127.0.0.1'",
+			args: args{
+				node: "127.0.0.1",
+			},
+			want: want{
+				want: New("discover node 127.0.0.1 not found"),
+			},
+		},
+		{
+			name: "returns discover node not found error when node is empty",
+			args: args{
+				node: "",
+			},
+			want: want{
+				want: New("discover node  not found"),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(tt *testing.T) {
+			if test.beforeFunc != nil {
+				test.beforeFunc(test.args)
+			}
+			if test.afterFunc != nil {
+				defer test.afterFunc(test.args)
+			}
+			if test.checkFunc == nil {
+				test.checkFunc = defaultCheckFunc
+			}
+
+			got := ErrNodeNotFound(test.args.node)
+			if err := test.checkFunc(test.want, got); err != nil {
+				tt.Errorf("error = %v", err)
+			}
+		})
+	}
+}
+
+func TestErrNamespaceNotFound(t *testing.T) {
+	type args struct {
+		ns string
+	}
+	type want struct {
+		want error
+	}
+	type test struct {
+		name       string
+		args       args
+		want       want
+		checkFunc  func(want, error) error
+		beforeFunc func(args)
+		afterFunc  func(args)
+	}
+	defaultCheckFunc := func(w want, got error) error {
+		if !Is(got, w.want) {
+			return Errorf("got: \"%#v\",\n\t\t\t\twant: \"%#v\"", got, w.want)
+		}
+		return nil
+	}
+	tests := []test{
+		{
+			name: "returns discover namespace not found error when ns is 'vald'",
+			args: args{
+				ns: "vald",
+			},
+			want: want{
+				want: New("discover namespace vald not found"),
+			},
+		},
+		{
+			name: "returns discover namespace not found error when ns is empty",
+			args: args{
+				ns: "",
+			},
+			want: want{
+				want: New("discover namespace  not found"),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(tt *testing.T) {
+			if test.beforeFunc != nil {
+				test.beforeFunc(test.args)
+			}
+			if test.afterFunc != nil {
+				defer test.afterFunc(test.args)
+			}
+			if test.checkFunc == nil {
+				test.checkFunc = defaultCheckFunc
+			}
+
+			got := ErrNamespaceNotFound(test.args.ns)
+			if err := test.checkFunc(test.want, got); err != nil {
+				tt.Errorf("error = %v", err)
+			}
+		})
+	}
+}
+
+func TestErrPodNameNotFound(t *testing.T) {
+	type args struct {
+		name string
+	}
+	type want struct {
+		want error
+	}
+	type test struct {
+		name       string
+		args       args
+		want       want
+		checkFunc  func(want, error) error
+		beforeFunc func(args)
+		afterFunc  func(args)
+	}
+	defaultCheckFunc := func(w want, got error) error {
+		if !Is(got, w.want) {
+			return Errorf("got: \"%#v\",\n\t\t\t\twant: \"%#v\"", got, w.want)
+		}
+		return nil
+	}
+	tests := []test{
+		{
+			name: "returns discover pod not found error when ns is 'vald-discoverer'",
+			args: args{
+				name: "vald-discoverer",
+			},
+			want: want{
+				want: New("discover pod vald-discoverer not found"),
+			},
+		},
+		{
+			name: "returns discover pod not found error when name is empty",
+			args: args{
+				name: "",
+			},
+			want: want{
+				want: New("discover pod  not found"),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(tt *testing.T) {
+			if test.beforeFunc != nil {
+				test.beforeFunc(test.args)
+			}
+			if test.afterFunc != nil {
+				defer test.afterFunc(test.args)
+			}
+			if test.checkFunc == nil {
+				test.checkFunc = defaultCheckFunc
+			}
+
+			got := ErrPodNameNotFound(test.args.name)
+			if err := test.checkFunc(test.want, got); err != nil {
+				tt.Errorf("error = %v", err)
+			}
+		})
+	}
+}
+
+func TestErrInvalidDiscoveryCache(t *testing.T) {
+	type want struct {
+		want error
+	}
+	type test struct {
+		name       string
+		want       want
+		checkFunc  func(want, error) error
+		beforeFunc func()
+		afterFunc  func()
+	}
+	defaultCheckFunc := func(w want, got error) error {
+		if !Is(got, w.want) {
+			return Errorf("got: \"%#v\",\n\t\t\t\twant: \"%#v\"", got, w.want)
+		}
+		return nil
+	}
+	tests := []test{
+		{
+			name: "returns cache type cast error",
+			want: want{
+				want: New("cache type cast failed"),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(tt *testing.T) {
+			if test.beforeFunc != nil {
+				test.beforeFunc()
+			}
+			if test.afterFunc != nil {
+				defer test.afterFunc()
+			}
+			if test.checkFunc == nil {
+				test.checkFunc = defaultCheckFunc
+			}
+
+			got := ErrInvalidDiscoveryCache
+			if err := test.checkFunc(test.want, got); err != nil {
+				tt.Errorf("error = %v", err)
+			}
+		})
+	}
+}