dbusutil/dbustest: add tests for TestBus and Suite

Test helpers are just code that also needs to be tested. Add smoke test
for TestBus and for the Suite types.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>

dbusutil/dbustest/dbustest_test.go

+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Huawei Inc.
+
+package dbustest_test
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+
+	. "gopkg.in/check.v1"
+
+	"git.ostc-eu.org/OSTC/OHOS/components/sysota/dbusutil/dbustest"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type testbusSuite struct{}
+
+var _ = Suite(&testbusSuite{})
+
+func (s *testbusSuite) TestNewTestBus(c *C) {
+	_, err := exec.LookPath("dbus-daemon")
+	if err != nil {
+		c.Skip(fmt.Sprintf("cannot initialize TestBus: %v", err))
+	}
+
+	bus, err := dbustest.NewTestBus()
+	c.Assert(err, IsNil)
+
+	defer func() {
+		c.Check(bus.Close(), IsNil)
+	}()
+
+	addr := bus.BusAddress()
+	c.Check(strings.HasPrefix(addr, "unix:path=/tmp/test-bus-"), Equals, true)
+}
+
+func (s *testbusSuite) TestSetDBusSystemBusAddress(c *C) {
+	restore, err := dbustest.SetDBusSystemBusAddress("potato")
+	c.Assert(err, IsNil)
+
+	defer func() {
+		c.Assert(restore(), IsNil)
+	}()
+
+	c.Check(os.Getenv("DBUS_SYSTEM_BUS_ADDRESS"), Equals, "potato")
+}
+
+type suiteSuite struct {
+	dbustest.Suite
+}
+
+var _ = Suite(&suiteSuite{})
+
+func (s *suiteSuite) TestSystemBusAddress(c *C) {
+	// Tests see a test system bus.
+	addr := os.Getenv("DBUS_SYSTEM_BUS_ADDRESS")
+	c.Check(strings.HasPrefix(addr, "unix:path=/tmp/test-bus-"), Equals, true)
+}