Restore flags to original values on test completion (#470)

## Changes

This is necessary to avoid test interference.

## Tests

Manually.

---------

Co-authored-by: Pieter Noordhuis <pieter.noordhuis@databricks.com>

internal/helpers.go

@@ -9,6 +9,7 @@ import (
 	"math/rand"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strings"
 	"sync"
 	"testing"
@@ -16,6 +17,8 @@ import (
 
 	"github.com/databricks/cli/cmd/root"
 	_ "github.com/databricks/cli/cmd/version"
+	"github.com/spf13/cobra"
+	"github.com/spf13/pflag"
 	"github.com/stretchr/testify/require"
 
 	_ "github.com/databricks/cli/cmd/workspace"
@@ -82,6 +85,33 @@ func consumeLines(ctx context.Context, wg *sync.WaitGroup, r io.Reader) <-chan s
 	return ch
 }
 
+func (t *cobraTestRunner) registerFlagCleanup(c *cobra.Command) {
+	// Find target command that will be run. Example: if the command run is `databricks fs cp`,
+	// target command corresponds to `cp`
+	targetCmd, _, err := c.Find(t.args)
+	require.NoError(t, err)
+
+	// Force initialization of default flags.
+	// These are initialized by cobra at execution time and would otherwise
+	// not be cleaned up by the cleanup function below.
+	targetCmd.InitDefaultHelpFlag()
+	targetCmd.InitDefaultVersionFlag()
+
+	// Restore flag values to their original value on test completion.
+	targetCmd.Flags().VisitAll(func(f *pflag.Flag) {
+		v := reflect.ValueOf(f.Value)
+		if v.Kind() == reflect.Ptr {
+			v = v.Elem()
+		}
+		// Store copy of the current flag value.
+		reset := reflect.New(v.Type()).Elem()
+		reset.Set(v)
+		t.Cleanup(func() {
+			v.Set(reset)
+		})
+	})
+}
+
 func (t *cobraTestRunner) RunBackground() {
 	var stdoutR, stderrR io.Reader
 	var stdoutW, stderrW io.WriteCloser
@@ -92,6 +122,12 @@ func (t *cobraTestRunner) RunBackground() {
 	root.SetErr(stderrW)
 	root.SetArgs(t.args)
 
+	// Register cleanup function to restore flags to their original values
+	// once test has been executed. This is needed because flag values reside
+	// in a global singleton data-structure, and thus subsequent tests might
+	// otherwise interfere with each other
+	t.registerFlagCleanup(root)
+
 	errch := make(chan error)
 	ctx, cancel := context.WithCancel(context.Background())