improve validate testing with examples

also simplified structure of test cases and failure logging

email_test.go

@@ -2,27 +2,45 @@ package validate
 
 import (
 	"errors"
+	"fmt"
 	"testing"
 )
 
-func TestEmail(t *testing.T) {
-	type TestCase struct {
-		Input string
-		Err   error
-	}
+func ExampleEmail() {
+	fmt.Println(Email("not an email"))
+	// Output: invalid email address
+}
 
-	testCases := []TestCase{
-		{Input: "test@example.com"},
-		{Input: "testexample.com", Err: ErrInvalidEmail},
-	}
+func FuzzEmail(f *testing.F) {
+	want := ErrInvalidEmail
 
-	for n, tc := range testCases {
-		t.Logf("(%d) Testing %q", n, tc.Input)
+	f.Fuzz(func(t *testing.T, input string) {
+		got := Email(input)
 
-		err := Email(tc.Input)
-
-		if !errors.Is(err, tc.Err) {
-			t.Errorf("Expected error %v, got %v", tc.Err, err)
+		if !errors.Is(got, want) {
+			t.Error("got", got)
+			t.Error("want", want)
 		}
+	})
+}
+
+func TestEmail(t *testing.T) {
+	testCases := map[string]error{
+		"test@example.com":                      nil,
+		"firstname.lastname@some-website.co.uk": nil,
+
+		"not an email":    ErrInvalidEmail,
+		"testexample.com": ErrInvalidEmail,
+	}
+
+	for input, want := range testCases {
+		t.Run(input, func(t *testing.T) {
+			got := Email(input)
+
+			if !errors.Is(got, want) {
+				t.Error("got", got)
+				t.Error("want", want)
+			}
+		})
 	}
 }