Table-driven tests with Testify assertions

package main

import (
	"errors"
	"strings"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

// NormalizeEmail is the production helper under test.
func NormalizeEmail(raw string) (string, error) {
	value := strings.ToLower(strings.TrimSpace(raw))
	if !strings.Contains(value, "@") || strings.HasPrefix(value, "@") {
		return "", errors.New("invalid email address")
	}
	return value, nil
}

func TestNormalizeEmail(t *testing.T) {
	tests := []struct {
		name    string
		input   string
		want    string
		wantErr bool
	}{
		{"lowercases and trims", "  [email protected] ", "[email protected]", false},
		{"missing at sign", "ada.example.com", "", true},
		{"only domain part", "@example.com", "", true},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			got, err := NormalizeEmail(tc.input)
			require.Equal(t, tc.wantErr, err != nil)
			assert.Equal(t, tc.want, got)
		})
	}
}