Allow single node clusters to override port

Previously, the port option could only be overridden if you were
running multiple cockroach nodes. This commit changes the behavior such
that you can override from port `0` to any arbitrary port in the single
node configuration.

testserver/testserver.go

@@ -405,7 +405,7 @@ func NewTestServer(opts ...TestServerOpt) (TestServer, error) {
 			serverArgs.numNodes, len(serverArgs.listenAddrPorts)))
 	}
 
-	if len(serverArgs.listenAddrPorts) == 0 || len(serverArgs.listenAddrPorts) == 1 {
+	if len(serverArgs.listenAddrPorts) == 0 {
 		serverArgs.listenAddrPorts = []int{0}
 	}
 
@@ -554,7 +554,7 @@ func NewTestServer(opts ...TestServerOpt) (TestServer, error) {
 				"--logtostderr",
 				secureOpt,
 				"--host=localhost",
-				"--port=0",
+				"--port=" + strconv.Itoa(serverArgs.listenAddrPorts[0]),
 				"--http-port=" + strconv.Itoa(serverArgs.httpPorts[0]),
 				storeArg,
 				"--listening-url-file=" + nodes[i].listeningURLFile,

testserver/testserver_test.go

@@ -25,6 +25,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"strconv"
 	"strings"
 	"sync"
 	"testing"
@@ -293,6 +294,30 @@ func TestPGURLWhitespace(t *testing.T) {
 	}
 }
 
+func TestSingleNodePort(t *testing.T) {
+	port, err := getFreePort()
+	require.NoError(t, err)
+
+	ts, err := testserver.NewTestServer(testserver.AddListenAddrPortOpt(port))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ts.Stop()
+
+	// check that port overriding worked
+	url := ts.PGURL()
+	require.Equal(t, strconv.Itoa(port), url.Port())
+
+	db, err := sql.Open("postgres", url.String())
+	require.NoError(t, err)
+
+	// check that connection was successful
+	var out int
+	row := db.QueryRow("SELECT 1")
+	require.NoError(t, row.Scan(&out))
+	require.Equal(t, 1, out)
+}
+
 // tenantInterface is defined in order to use tenant-related methods on the
 // TestServer.
 type tenantInterface interface {