test: make TestExit_Unwrap table-driven

Check each kind of Exit message (an error, an error chain and a
non-error message) with errors.Unwrap, and with errors.Is and errors.As
where they apply.

Drop the errors.As check to ExitCoder, which also passes without Unwrap
because Exit returns the ExitCoder itself. The error chain case checks
errors.As to the wrapped *fs.PathError instead, which only passes when
Unwrap is in place.

Assisted-by: claude:claude-opus-5-5
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

Author: Juneezee

errors_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"io/fs"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -274,18 +275,45 @@ func TestHandleExitCoder_ExitCoderEmptyMessage(t *testing.T) {
 func TestExit_Unwrap(t *testing.T) {
 	sentinel := errors.New("not found")
 
-	err := Exit(sentinel, 2)
-
 	// The error given to Exit must stay reachable through the standard
 	// wrapping helpers (#1090).
-	assert.ErrorIs(t, err, sentinel)
-	assert.Equal(t, sentinel, errors.Unwrap(err))
-
-	var ec ExitCoder
-	assert.True(t, errors.As(err, &ec))
-	assert.Equal(t, 2, ec.ExitCode())
-
-	// A non-error message is wrapped into a fresh error and still unwraps.
-	err = Exit("boom", 3)
-	assert.EqualError(t, errors.Unwrap(err), "boom")
+	tests := []struct {
+		name    string
+		message any
+		wantMsg string // message of errors.Unwrap(err)
+		wantIs  error  // target for errors.Is, if any
+		wantAs  any    // target for errors.As, if any
+	}{
+		{
+			name:    "error",
+			message: sentinel,
+			wantMsg: "not found",
+			wantIs:  sentinel,
+		},
+		{
+			name:    "error chain",
+			message: &fs.PathError{Op: "open", Path: "x", Err: fs.ErrNotExist},
+			wantMsg: "open x: file does not exist",
+			wantIs:  fs.ErrNotExist,
+			wantAs:  new(*fs.PathError),
+		},
+		{
+			name:    "non-error message",
+			message: "boom",
+			wantMsg: "boom",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := Exit(tt.message, 2)
+
+			assert.EqualError(t, errors.Unwrap(err), tt.wantMsg)
+			if tt.wantIs != nil {
+				assert.ErrorIs(t, err, tt.wantIs)
+			}
+			if tt.wantAs != nil {
+				assert.ErrorAs(t, err, tt.wantAs)
+			}
+		})
+	}
 }