channeldb: move makeTestDB out of test to make it available for other tests

This commit moves makeTestDB to db.go and exports it so that we'll be
able to use this function in other unit tests to make them testable with
etcd if needed.

channeldb/db.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/binary"
 	"fmt"
+	"io/ioutil"
 	"net"
 	"os"
 
@@ -1260,3 +1261,37 @@ func (db *DB) FetchHistoricalChannel(outPoint *wire.OutPoint) (*OpenChannel, err
 
 	return channel, nil
 }
+
+// MakeTestDB creates a new instance of the ChannelDB for testing purposes.
+// A callback which cleans up the created temporary directories is also
+// returned and intended to be executed after the test completes.
+func MakeTestDB(modifiers ...OptionModifier) (*DB, func(), error) {
+	// First, create a temporary directory to be used for the duration of
+	// this test.
+	tempDirName, err := ioutil.TempDir("", "channeldb")
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// Next, create channeldb for the first time.
+	backend, backendCleanup, err := kvdb.GetTestBackend(tempDirName, "cdb")
+	if err != nil {
+		backendCleanup()
+		return nil, nil, err
+	}
+
+	cdb, err := CreateWithBackend(backend, modifiers...)
+	if err != nil {
+		backendCleanup()
+		os.RemoveAll(tempDirName)
+		return nil, nil, err
+	}
+
+	cleanUp := func() {
+		cdb.Close()
+		backendCleanup()
+		os.RemoveAll(tempDirName)
+	}
+
+	return cdb, cleanUp, nil
+}