diff --git a/helper_test.go b/helper_test.go
index 7da80b9..0d4b2ce 100644
--- a/helper_test.go
+++ b/helper_test.go
@@ -12,13 +12,13 @@ const wantBase64 = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAHEAAABxCAYAAA
 
 func TestBase64EncodeFileName(t *testing.T) {
 	// Error in os.Open.
-	uri, err := Base64EncodeFileName("fail")
+	_, err := Base64EncodeFileName("fail")
 	if err == nil {
 		t.Fatalf("should be fail: %v", err)
 	}
 
 	// Success.
-	uri, err = Base64EncodeFileName("testdata/logo.png")
+	uri, err := Base64EncodeFileName("testdata/logo.png")
 	if err != nil {
 		t.Fatalf("should not be fail: %v", err)
 	}
@@ -29,7 +29,7 @@ func TestBase64EncodeFileName(t *testing.T) {
 
 func TestBase64Encode(t *testing.T) {
 	// Error in file.Stat.
-	uri, err := Base64Encode(nil)
+	_, err := Base64Encode(nil)
 	if err == nil {
 		t.Fatalf("should be fail: %v", err)
 	}
@@ -43,7 +43,7 @@ func TestBase64Encode(t *testing.T) {
 	if err != nil {
 		t.Fatalf("should not be fail: %v", err)
 	}
-	uri, err = Base64Encode(logo)
+	_, err = Base64Encode(logo)
 	if err == nil {
 		t.Fatalf("should be fail: %v", err)
 	}
@@ -53,7 +53,7 @@ func TestBase64Encode(t *testing.T) {
 	if err != nil {
 		t.Fatalf("should not be fail: %v", err)
 	}
-	uri, err = Base64Encode(logo)
+	uri, err := Base64Encode(logo)
 	if err != nil {
 		t.Fatalf("should not be fail: %v", err)
 	}
diff --git a/lists_test.go b/lists_test.go
index ec98cc7..b6f400e 100644
--- a/lists_test.go
+++ b/lists_test.go
@@ -57,11 +57,11 @@ func TestGetAccountLists(t *testing.T) {
 		ClientSecret: "bar",
 		AccessToken:  "zoo",
 	})
-	lists, err := client.GetAccountLists(context.Background(), "2")
+	_, err := client.GetAccountLists(context.Background(), "2")
 	if err == nil {
 		t.Fatalf("should be fail: %v", err)
 	}
-	lists, err = client.GetAccountLists(context.Background(), "1")
+	lists, err := client.GetAccountLists(context.Background(), "1")
 	if err != nil {
 		t.Fatalf("should not be fail: %v", err)
 	}
@@ -93,11 +93,11 @@ func TestGetListAccounts(t *testing.T) {
 		ClientSecret: "bar",
 		AccessToken:  "zoo",
 	})
-	accounts, err := client.GetListAccounts(context.Background(), "2")
+	_, err := client.GetListAccounts(context.Background(), "2")
 	if err == nil {
 		t.Fatalf("should be fail: %v", err)
 	}
-	accounts, err = client.GetListAccounts(context.Background(), "1")
+	accounts, err := client.GetListAccounts(context.Background(), "1")
 	if err != nil {
 		t.Fatalf("should not be fail: %v", err)
 	}
diff --git a/status_test.go b/status_test.go
index d6120d0..7536ffb 100644
--- a/status_test.go
+++ b/status_test.go
@@ -609,6 +609,9 @@ func TestUploadMedia(t *testing.T) {
 		t.Fatalf("want %q but %q", "123", attachment.ID)
 	}
 	file, err := os.Open("testdata/logo.png")
+	if err != nil {
+		t.Fatalf("could not open file: %v", err)
+	}
 	defer file.Close()
 	writerAttachment, err := client.UploadMediaFromReader(context.Background(), file)
 	if err != nil {
diff --git a/streaming_ws_test.go b/streaming_ws_test.go
index cf60530..856702a 100644
--- a/streaming_ws_test.go
+++ b/streaming_ws_test.go
@@ -243,12 +243,12 @@ func TestDial(t *testing.T) {
 		t.Fatalf("should be fail: %v", err)
 	}
 
-	_, rawurl, err := client.dial("ws://" + ts.Listener.Addr().String())
+	_, _, err = client.dial("ws://" + ts.Listener.Addr().String())
 	if err == nil {
 		t.Fatalf("should be fail: %v", err)
 	}
 
-	_, rawurl, err = client.dial("ws://" + ts.Listener.Addr().String())
+	_, rawurl, err := client.dial("ws://" + ts.Listener.Addr().String())
 	if err != nil {
 		t.Fatalf("should not be fail: %v", err)
 	}