test(general): fix TestSnapshotNoLeftoverCheckpoints slowness (#4611)

Avoid allocating 1GB of RAM to write a test file.
Exclude test from race detector.

- Fixes: #4610
- Ref: #4439

nits:
- use `require.Greater`.
- add types to constants to used them with `require.*`.
- factor out function to write file with random data.

tests/end_to_end_test/norace_test.go

@@ -0,0 +1,73 @@
+//go:build !race
+// +build !race
+
+package endtoend_test
+
+import (
+	"io"
+	"math/rand"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/kopia/kopia/internal/clock"
+	"github.com/kopia/kopia/internal/testutil"
+	"github.com/kopia/kopia/tests/clitestutil"
+	"github.com/kopia/kopia/tests/testenv"
+)
+
+// Exclude tests below from the -race detection test, because they are resource
+// intensive and way too slow.
+
+func TestSnapshotNoLeftoverCheckpoints(t *testing.T) {
+	// 1 GiB of data seems to be enough for the snapshot time to exceed one second.
+	const (
+		fileSize                  = int64(1) << 30
+		checkpointInterval        = "1s"
+		checkpointIntervalSeconds = float64(1)
+	)
+
+	t.Parallel()
+
+	runner := testenv.NewInProcRunner(t)
+	e := testenv.NewCLITest(t, testenv.RepoFormatNotImportant, runner)
+
+	defer e.RunAndExpectSuccess(t, "repo", "disconnect")
+
+	e.RunAndExpectSuccess(t, "repo", "create", "filesystem", "--path", e.RepoDir)
+
+	baseDir := testutil.TempDirectory(t)
+	writeRandomFile(t, filepath.Join(baseDir, "foo"), fileSize)
+
+	startTime := clock.Now()
+
+	e.RunAndExpectSuccess(t, "snapshot", "create", baseDir, "--checkpoint-interval", checkpointInterval)
+
+	require.Greater(t, clock.Now().Sub(startTime).Seconds(), checkpointIntervalSeconds)
+
+	// This exploits the implementation detail of `ListSnapshotsAndExpectSuccess`, that it does
+	// not sanitize `targets` to exclude flags.
+	si := clitestutil.ListSnapshotsAndExpectSuccess(t, e, "--incomplete", baseDir)
+	require.Len(t, si, 1)
+	require.Len(t, si[0].Snapshots, 1)
+	require.False(t, si[0].Snapshots[0].Incomplete)
+}
+
+func writeRandomFile(t *testing.T, name string, fileSize int64) {
+	t.Helper()
+
+	f, err := os.Create(name)
+
+	require.NoError(t, err)
+	require.NotNil(t, f)
+
+	defer func() {
+		require.NoError(t, f.Close())
+	}()
+
+	n, err := io.CopyN(f, rand.New(rand.NewSource(0)), fileSize)
+	require.NoError(t, err)
+	require.Equal(t, fileSize, n)
+}

tests/end_to_end_test/snapshot_create_test.go

@@ -1,7 +1,6 @@
 package endtoend_test
 
 import (
-	"math/rand"
 	"os"
 	"path"
 	"path/filepath"
@@ -18,7 +17,6 @@
 
 	"github.com/kopia/kopia/cli"
 	"github.com/kopia/kopia/internal/cachedir"
-	"github.com/kopia/kopia/internal/clock"
 	"github.com/kopia/kopia/internal/testutil"
 	"github.com/kopia/kopia/snapshot"
 	"github.com/kopia/kopia/snapshot/policy"
@@ -801,61 +799,3 @@ func TestSnapshotCreateWithAllAndPath(t *testing.T) {
 	e.RunAndExpectSuccess(t, "snapshot", "create", sharedTestDataDir2)
 	e.RunAndExpectFailure(t, "snapshot", "create", sharedTestDataDir1, "--all")
 }
-
-func TestSnapshotNoLeftoverCheckpoints(t *testing.T) {
-	// 1 GiB of data seems to be enough for the snapshot time to exceed one second.
-	const (
-		fileSize                  = 1 << 30
-		checkpointInterval        = "1s"
-		checkpointIntervalSeconds = 1
-	)
-
-	t.Parallel()
-
-	runner := testenv.NewInProcRunner(t)
-	e := testenv.NewCLITest(t, testenv.RepoFormatNotImportant, runner)
-
-	defer e.RunAndExpectSuccess(t, "repo", "disconnect")
-
-	e.RunAndExpectSuccess(t, "repo", "create", "filesystem", "--path", e.RepoDir)
-
-	baseDir := testutil.TempDirectory(t)
-	files := []testFileEntry{
-		{
-			Name: "/foo",
-			Content: []string{
-				generateRandomLetters(fileSize),
-			},
-		},
-	}
-
-	require.NoError(t, createFileStructure(baseDir, files))
-
-	startTime := clock.Now()
-
-	e.RunAndExpectSuccess(t, "snapshot", "create", baseDir, "--checkpoint-interval", checkpointInterval)
-
-	endTime := clock.Now()
-
-	snapshotTimeSurpassedCheckpointInterval := endTime.Sub(startTime).Seconds() > checkpointIntervalSeconds
-	require.True(t, snapshotTimeSurpassedCheckpointInterval)
-
-	// This exploits the implementation detail of `ListSnapshotsAndExpectSuccess`, that it does
-	// not sanitize `targets` to exclude flags.
-	si := clitestutil.ListSnapshotsAndExpectSuccess(t, e, "--incomplete", baseDir)
-	require.Len(t, si, 1)
-	require.Len(t, si[0].Snapshots, 1)
-	require.False(t, si[0].Snapshots[0].Incomplete)
-}
-
-// https://stackoverflow.com/a/31832326
-func generateRandomLetters(n int) string {
-	const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
-
-	b := make([]byte, n)
-	for i := range b {
-		b[i] = letterBytes[rand.Int63()%int64(len(letterBytes))]
-	}
-
-	return string(b)
-}