go/zodb/fs1: tests: Factor-out checking for Python/ZODB presence into common place

We will soon need to check for Python and other modules in more tests.
Now the checking function is generic - see xtesting.NeedPy docs.

go/internal/README

+// internal/ is a staging place for common utilities not yet sorted out
+// to their proper homes.

go/internal/xtesting/xtesting.go

+// Copyright (C) 2017-2019  Nexedi SA and Contributors.
+//                          Kirill Smelkov <kirr@nexedi.com>
+//
+// This program is free software: you can Use, Study, Modify and Redistribute
+// it under the terms of the GNU General Public License version 3, or (at your
+// option) any later version, as published by the Free Software Foundation.
+//
+// You can also Link and Combine this program with other software covered by
+// the terms of any of the Free Software licenses or any of the Open Source
+// Initiative approved licenses and Convey the resulting work. Corresponding
+// source of such a combination shall include the source code for all other
+// software used.
+//
+// This program is distributed WITHOUT ANY WARRANTY; without even the implied
+// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+//
+// See COPYING file for full licensing terms.
+// See https://www.nexedi.com/licensing for rationale and options.
+
+// Package xtesting provides addons to std package testing.
+package xtesting
+
+import (
+	"os/exec"
+	"sync"
+	"testing"
+)
+
+var (
+	pyMu   sync.Mutex
+	pyHave = map[string]bool{} // {} pymod -> y/n  ; ".python" indicates python presence
+)
+
+// NeedPy skips current test if python and specified modules are not available.
+//
+// For example
+//
+//	xtesting.NeedPy(t)
+//
+// would check for python presence, and
+//
+//	xtesting.NeedPy(t, "ZODB", "golang.strconv")
+//
+// would check if all python and ZODB and golang.strconv python modules are available.
+func NeedPy(t testing.TB, modules ...string) {
+	pyMu.Lock()
+	defer pyMu.Unlock()
+
+	// verify if python is present
+	havePy, know := pyHave[".python"]
+	if !know {
+		cmd := exec.Command("python2", "-c", "0")
+		err := cmd.Run()
+		havePy = (err == nil)
+		pyHave[".python"] = havePy
+	}
+
+	if !havePy {
+		t.Skipf("skipping: python is not availble")
+	}
+
+	var donthave []string
+	for _, pymod := range modules {
+		have, know := pyHave[pymod]
+		if !know {
+			cmd := exec.Command("python2", "-c", "import "+pymod)
+			err := cmd.Run()
+			have = (err == nil)
+			pyHave[pymod] = have
+		}
+		if !have {
+			donthave = append(donthave, pymod)
+		}
+	}
+
+	if len(donthave) != 0 {
+		t.Skipf("skipping: the following python modules are not available: %s", donthave)
+	}
+
+	// we verified everything - now it is ok not to skip.
+	return
+}

go/zodb/storage/fs1/index_test.go

-// Copyright (C) 2017  Nexedi SA and Contributors.
+// Copyright (C) 2017-2019  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This program is free software: you can Use, Study, Modify and Redistribute
@@ -32,6 +32,7 @@ import (
 	"strings"
 	"testing"
 
+	"lab.nexedi.com/kirr/neo/go/internal/xtesting"
 	"lab.nexedi.com/kirr/neo/go/zodb"
 	"lab.nexedi.com/kirr/neo/go/zodb/storage/fs1/fsb"
 )
@@ -201,7 +202,7 @@ func TestIndexLoadFromPy(t *testing.T) {
 
 // test zodb/py can read index data as saved by us
 func TestIndexSaveToPy(t *testing.T) {
-	needZODBPy(t)
+	xtesting.NeedPy(t, "ZODB")
 	workdir := xworkdir(t)
 
 	err := _1fs_index.SaveFile(workdir + "/1.fs.index")
@@ -289,19 +290,11 @@ func BenchmarkIndexGet(b *testing.B) {
 	}
 }
 
-var haveZODBPy = false
 var workRoot string
 
 func TestMain(m *testing.M) {
-	// check whether we have zodb/py
-	cmd := exec.Command("python2", "-c", "import ZODB")
-	err := cmd.Run()
-	if err == nil {
-		haveZODBPy = true
-	}
-
 	// setup work root for all tests
-	workRoot, err = ioutil.TempDir("", "t-index")
+	workRoot, err := ioutil.TempDir("", "t-index")
 	if err != nil {
 		log.Fatal(err)
 	}
@@ -313,13 +306,6 @@ func TestMain(m *testing.M) {
 	os.Exit(exit)
 }
 
-func needZODBPy(t *testing.T) {
-	if haveZODBPy {
-		return
-	}
-	t.Skipf("skipping: zodb/py is not available")
-}
-
 // create temp dir inside workRoot
 func xworkdir(t testing.TB) string {
 	work, err := ioutil.TempDir(workRoot, "")