tests: add unit tests for UPN validation

Add comprehensive unit tests for is_valid_upn() function in
`tests/unit/test_chkname.c` covering:
- Valid UPN formats (user@domain.com)
- Invalid structures (missing @, multiple @)
- Domain validation (RFC compliance)
- Boundary limits (253/254 char domains, 63+ char labels)

Signed-off-by: Iker Pedrosa <ipedrosa@redhat.com>

Author: ikerexxe

tests/unit/test_chkname.c

@@ -29,6 +29,12 @@ static void test_is_valid_user_name_nok_empty(MAYBE_UNUSED void ** _1);
 static void test_is_valid_user_name_nok_numeric(MAYBE_UNUSED void ** _1);
 static void test_is_valid_user_name_nok_otherchars(MAYBE_UNUSED void ** _1);
 static void test_is_valid_user_name_long(MAYBE_UNUSED void ** _1);
+static void test_is_valid_upn_ok(MAYBE_UNUSED void ** _1);
+static void test_is_valid_upn_nok_not_upn(MAYBE_UNUSED void ** _1);
+static void test_is_valid_upn_nok_structure(MAYBE_UNUSED void ** _1);
+static void test_is_valid_upn_nok_domain(MAYBE_UNUSED void ** _1);
+static void test_is_valid_upn_ok_limits(MAYBE_UNUSED void ** _1);
+static void test_is_valid_upn_nok_limits(MAYBE_UNUSED void ** _1);
 
 
 int
@@ -44,6 +50,12 @@ main(void)
         cmocka_unit_test(test_is_valid_user_name_nok_numeric),
         cmocka_unit_test(test_is_valid_user_name_nok_otherchars),
         cmocka_unit_test(test_is_valid_user_name_long),
+        cmocka_unit_test(test_is_valid_upn_ok),
+        cmocka_unit_test(test_is_valid_upn_nok_not_upn),
+        cmocka_unit_test(test_is_valid_upn_nok_structure),
+        cmocka_unit_test(test_is_valid_upn_nok_domain),
+        cmocka_unit_test(test_is_valid_upn_ok_limits),
+        cmocka_unit_test(test_is_valid_upn_nok_limits),
     };
 
     return cmocka_run_group_tests(tests, NULL, NULL);
@@ -147,3 +159,123 @@ test_is_valid_user_name_long(MAYBE_UNUSED void ** _1)
 
 	free(name);
 }
+
+
+static void
+test_is_valid_upn_ok(MAYBE_UNUSED void ** _1)
+{
+	assert_true(is_valid_upn("user@example.com"));
+	assert_true(is_valid_upn("john.doe@corp.example.org"));
+	assert_true(is_valid_upn("test@sub.domain.net"));
+	assert_true(is_valid_upn("a@b.c"));
+	assert_true(is_valid_upn("user123@test123.example"));
+	assert_true(is_valid_upn("user_name@example-domain.com"));
+	assert_true(is_valid_upn("test.user@example.domain.org"));
+}
+
+
+static void
+test_is_valid_upn_nok_not_upn(MAYBE_UNUSED void ** _1)
+{
+	assert_true(false == is_valid_upn("regularuser"));
+	assert_true(false == is_valid_upn("user.name"));
+	assert_true(false == is_valid_upn("user_name"));
+	assert_true(false == is_valid_upn("123user"));
+	assert_true(false == is_valid_upn("USER"));
+}
+
+
+static void
+test_is_valid_upn_nok_structure(MAYBE_UNUSED void ** _1)
+{
+	// Empty parts
+	assert_true(false == is_valid_upn("@domain.com"));
+	assert_true(false == is_valid_upn("user@"));
+	assert_true(false == is_valid_upn("@"));
+
+	// Multiple @ symbols
+	assert_true(false == is_valid_upn("user@domain@com"));
+	assert_true(false == is_valid_upn("@@domain.com"));
+	assert_true(false == is_valid_upn("user@@domain.com"));
+
+	// Empty string
+	assert_true(false == is_valid_upn(""));
+
+	// Invalid suffix
+	assert_true(false == is_valid_upn("-user@domain.com"));
+	assert_true(false == is_valid_upn("123@domain.com"));
+	assert_true(false == is_valid_upn("user space@domain.com"));
+}
+
+
+static void
+test_is_valid_upn_nok_domain(MAYBE_UNUSED void ** _1)
+{
+	// Invalid domain formats
+	assert_true(false == is_valid_upn("user@domain"));
+	assert_true(false == is_valid_upn("user@.domain.com"));
+	assert_true(false == is_valid_upn("user@domain.com."));
+	assert_true(false == is_valid_upn("user@domain..com"));
+	assert_true(false == is_valid_upn("user@sub."));
+
+	// Invalid domain characters
+	assert_true(false == is_valid_upn("user@domain_name.com"));
+	assert_true(false == is_valid_upn("user@domain name.com"));
+}
+
+
+static void
+test_is_valid_upn_ok_limits(MAYBE_UNUSED void ** _1)
+{
+	char    *upn;
+	char    *domain;
+
+	// Test domain at maximum allowed length (253 chars)
+	domain = malloc_T(253 + 1, char);
+	assert_true(domain != NULL);
+	strcpy(domain,
+		"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa." // 63 a's + dot
+		"bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb." // 63 b's + dot
+		"ccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc." // 63 c's + dot
+		"dddddddddddddddddddddddddddddddddddddddddddddddddddddddddd."      // 58 d's + dot
+		"co");                                                             // 2
+	// Total: 63 + 1 + 63 + 1 + 63 + 1 + 58 + 1 + 2 = 253 chars
+
+	upn = malloc_T(5 + 253 + 1, char);  // "user@" + domain + '\0'
+	assert_true(upn != NULL);
+	strcpy(upn, "user@");
+	strcat(upn, domain);
+	assert_true(is_valid_upn(upn));
+
+	free(upn);
+	free(domain);
+}
+
+
+static void
+test_is_valid_upn_nok_limits(MAYBE_UNUSED void ** _1)
+{
+	char    *upn;
+	char    *domain;
+
+	// Test domain exceeding maximum length (254 chars)
+	domain = malloc_T(254 + 1, char);
+	assert_true(domain != NULL);
+	memset(domain, 'a', 251);
+	strcpy(&domain[251], ".co");
+	domain[254] = '\0';
+
+	upn = malloc_T(5 + 254 + 1, char);  // "user@" + domain + '\0'
+	assert_true(upn != NULL);
+	strcpy(upn, "user@");
+	strcat(upn, domain);
+	assert_true(false == is_valid_upn(upn));
+
+	free(upn);
+	free(domain);
+
+	// Domain label too long (>63 chars)
+	assert_true(false == is_valid_upn("user@"
+		"verylongdomainlabelthatexceedssixtythreecharacterslimitsetbyRFC1035"
+		".com"));
+}