Add a library.PinnipedCLIPath() test helper, with caching.

Caching saves us a little bit of time now that we're using the CLI in more and more tests.

Signed-off-by: Matt Moyer <moyerm@vmware.com>

test/library/cli.go

@@ -0,0 +1,45 @@
+// Copyright 2020 the Pinniped contributors. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package library
+
+import (
+	"io/ioutil"
+	"os/exec"
+	"path/filepath"
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"go.pinniped.dev/internal/testutil"
+)
+
+//nolint: gochecknoglobals
+var pinnipedCLIBinaryCache struct {
+	buf   []byte
+	mutex sync.Mutex
+}
+
+// PinnipedCLIPath returns the path to the Pinniped CLI binary, built on demand and cached between tests.
+func PinnipedCLIPath(t *testing.T) string {
+	t.Helper()
+	pinnipedCLIBinaryCache.mutex.Lock()
+	defer pinnipedCLIBinaryCache.mutex.Unlock()
+	path := filepath.Join(testutil.TempDir(t), "pinniped")
+	if pinnipedCLIBinaryCache.buf != nil {
+		t.Log("using previously built pinniped CLI binary")
+		require.NoError(t, ioutil.WriteFile(path, pinnipedCLIBinaryCache.buf, 0500))
+		return path
+	}
+
+	t.Log("building pinniped CLI binary")
+	output, err := exec.Command("go", "build", "-o", path, "go.pinniped.dev/cmd/pinniped").CombinedOutput()
+	require.NoError(t, err, string(output))
+
+	// Fill our cache so we don't have to do this again.
+	pinnipedCLIBinaryCache.buf, err = ioutil.ReadFile(path)
+	require.NoError(t, err, string(output))
+
+	return path
+}