Remove cleanup in testcli package (#2108)

## Changes

The main CLI entry point used to be a global variable, and the global
state had to be cleaned up after every test run. This hasn't been the
case for a while, and instead, the CLI is initialized in a function
call. State accumulated by a single CLI "instance" can no longer leak
into other instances, so we no longer have to perform cleanup.

## Tests

Existing tests pass.

internal/testcli/runner.go

@@ -6,13 +6,10 @@ import (
 	"context"
 	"encoding/json"
 	"io"
-	"reflect"
 	"strings"
 	"sync"
 	"time"
 
-	"github.com/spf13/cobra"
-	"github.com/spf13/pflag"
 	"github.com/stretchr/testify/require"
 
 	"github.com/databricks/cli/cmd"
@@ -68,39 +65,6 @@ func consumeLines(ctx context.Context, wg *sync.WaitGroup, r io.Reader) <-chan s
 	return ch
 }
 
-func (r *Runner) registerFlagCleanup(c *cobra.Command) {
-	r.Helper()
-	// 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(r.args)
-	if err != nil && strings.HasPrefix(err.Error(), "unknown command") {
-		// even if command is unknown, we can proceed
-		require.NotNil(r, targetCmd)
-	} else {
-		require.NoError(r, 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)
-		r.Cleanup(func() {
-			v.Set(reset)
-		})
-	})
-}
-
 // Like [Runner.Eventually], but more specific
 func (r *Runner) WaitForTextPrinted(text string, timeout time.Duration) {
 	r.Eventually(func() bool {
@@ -159,12 +123,6 @@ func (r *Runner) RunBackground() {
 		cli.SetIn(r.stdinR)
 	}
 
-	// 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
-	r.registerFlagCleanup(cli)
-
 	errch := make(chan error)
 	ctx, cancel := context.WithCancel(ctx)
 
@@ -208,12 +166,6 @@ func (r *Runner) RunBackground() {
 			}
 		}
 
-		// Reset context on command for the next test.
-		// These commands are globals so we have to clean up to the best of our ability after each run.
-		// See https://github.com/spf13/cobra/blob/a6f198b635c4b18fff81930c40d464904e55b161/command.go#L1062-L1066
-		//nolint:staticcheck  // cobra sets the context and doesn't clear it
-		cli.SetContext(nil)
-
 		// Make caller aware of error.
 		errch <- err
 		close(errch)