Add Dial tests (#83)

* Add DialOption tests
* Add Dial() error tests

conn_test.go

@@ -0,0 +1,58 @@
+// Copyright 2020 The mqtt-go authors.
+//
+// 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 mqtt
+
+import (
+	"errors"
+	"net"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/at-wat/mqtt-go/internal/errs"
+)
+
+func TestDialOptionError(t *testing.T) {
+	errExpected := errors.New("an error")
+	optErr := func() DialOption {
+		return func(o *DialOptions) error {
+			return errExpected
+		}
+	}
+
+	if _, err := Dial("mqtt://localhost:1883", optErr()); err != errExpected {
+		t.Errorf("Expected error: '%v', got: '%v'", errExpected, err)
+	}
+}
+
+func TestDialOption_WithDialer(t *testing.T) {
+	if _, err := Dial("mqtt://localhost:1884",
+		WithDialer(&net.Dialer{Timeout: time.Nanosecond}),
+	); !strings.Contains(err.Error(), "timeout") {
+		t.Errorf("Expected timeout error, got: '%v'", err)
+	}
+}
+
+func TestDial_UnsupportedProtocol(t *testing.T) {
+	if _, err := Dial("unknown://localhost:1884"); !errs.Is(err, ErrUnsupportedProtocol) {
+		t.Errorf("Expected error: '%v', got: '%v'", ErrUnsupportedProtocol, err)
+	}
+}
+
+func TestDial_InvalidURL(t *testing.T) {
+	if _, err := Dial("://localhost"); !strings.Contains(err.Error(), "missing protocol scheme") {
+		t.Errorf("Expected error: 'missing protocol scheme', got: '%v'", err)
+	}
+}