# Custom Tests

URL: /docs/extending/custom-tests/
Section: extending
Tags: extending, tests

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Custom Tests Tests are boolean predicates used with is in conditionals. Basic Test from kida import Environment env = Environment() def is_positive(value): return value > 0 env.add_test("positive", is_positive) Template usage: {% if count is positive %} {{ count }} items {% end %} Decorator Syntax @env.test() def is_even(value): return value % 2 == 0 @env.test("prime") # Custom name def is_prime_number(n): return n > 1 and all(n % i for i in range(2, int(n**0.5) + 1)) Template usage: {% if number is even %} {% if 17 is prime %} Tests with Arguments @env.test() def divisible_by(value, divisor): return value % divisor == 0 @env.test() def between(value, min_val, max_val): return min_val <= value <= max_val Template usage: {% if count is divisible_by(3) %} {% if score is between(0, 100) %} Negation Use is not to negate tests: {% if count is not even %} {% if user is not defined %} Built-in Tests Test Description defined Value is not None undefined Value is None none Value is None even Integer is even odd Integer is odd number Value is int or float string Value is a string sequence Value is list/tuple/string mapping Value is a dict iterable Value supports iteration callable Value is callable Common Patterns Type Tests @env.test() def is_list(value): return isinstance(value, list) @env.test() def is_dict(value): return isinstance(value, dict) @env.test() def is_empty(value): if value is None: return True try: return len(value) == 0 except TypeError: return False Value Tests @env.test() def is_blank(value): """Test if value is None, empty, or whitespace-only.""" if value is None: return True if isinstance(value, str): return not value.strip() try: return len(value) == 0 except TypeError: return False @env.test() def is_in_range(value, start, end): return start <= value <= end Object Tests @env.test() def is_admin(user): return getattr(user, "role", None) == "admin" @env.test() def is_published(post): return getattr(post, "status", None) == "published" @env.test() def has_children(page): children = getattr(page, "children", None) return bool(children) String Tests @env.test() def is_email(value): import re pattern = r'^[\w.-]+@[\w.-]+\.\w+$' return bool(re.match(pattern, str(value))) @env.test() def is_url(value): return str(value).startswith(("http://", "https://")) @env.test() def contains(value, substring): return substring in str(value) Batch Registration tests = { "positive": lambda x: x > 0, "negative": lambda x: x < 0, "zero": lambda x: x == 0, } env.update_tests(tests) Best Practices Return Boolean # ✅ Returns boolean @env.test() def is_valid(value): return bool(validate(value)) # ❌ Returns non-boolean @env.test() def is_valid(value): return validate(value) # Might return None Handle None @env.test() def is_active(value): if value is None: return False return getattr(value, "is_active", False) Descriptive Names # ✅ Clear purpose @env.test() def has_permission(user, permission): return permission in getattr(user, "permissions", []) # ❌ Vague @env.test() def check(value, x): ... See Also Built-in Tests — All built-in tests Control Flow — Using tests in conditionals Custom Filters — Transform values

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