Assertion Engine

Generic way to create meaningful and easy to use assertions for the Robot Framework libraries. This tool is a spin off from the Browser library project, where the Assertion Engine was developed as part of that library.

Supported Assertions

Currently supported assertion operators are:

| Operator | Alternative Operators | Description | Validate Equivalent | |---|---|---|---| | == | equal, equals, should be | Checks if returned value is equal to expected value. | value == expected | | != | inequal, should not be | Checks if returned value is not equal to expected value. | value != expected | | > | greater than | Checks if returned value is greater than expected value. | value > expected | | >= | | Checks if returned value is greater than or equal to expected value. | value >= expected | | < | less than | Checks if returned value is less than expected value. | value < expected | | <= | | Checks if returned value is less than or equal to expected value. | value <= expected | | *= | contains | Checks if returned value contains expected value as substring. | expected in value | | (no operator) | not contains | Checks if returned value does not contain expected value as substring. | expected not in value | | ^= | should start with, starts | Checks if returned value starts with expected value. | re.search(f"^{expected}", value) | | $= | should end with, ends | Checks if returned value ends with expected value. | re.search(f"{expected}$", value) | | matches | | Checks if given RegEx matches minimum once in returned value (supports Python Regex inline flags). | re.search(expected, value) | | validate | | Checks if given Python expression evaluates to True. | | | evaluate / then | | When using this operator, the keyword returns the evaluated Python expression. | |

Supported formatters

| Formatter | Description | |---|---| | normalize spaces | Substitutes multiple spaces to single space from the value | | strip | Removes spaces from the beginning and end of the value | | apply to expected | Applies rules also for the expected value | | case insensitive | Converts value to lower case |

Usage

When library developers want to do an assertion inline with the keyword call, AssertionEngine provides automatic validation within a single keyword call. The keyword method should get the value (for example from a page, database or any other source) and then use verify_assertion from AssertionEngine to perform the validation. The verify_assertion method needs three things to perform the assertion: the value from the system, an assertion_operator describing how the validation is performed and assertion_expected which represents the expected value. It is also possible to provide a custom error message and prefix the default error message.

Example:

def keyword(
    arg_to_get_value: str,
    assertion_operator: Optional[AssertionOperator] = None,
    assertion_expected: Any = None,
    message: str = None,
):
    value = method_to_get_value(arg_to_get_value)
    return verify_assertion(
        value,
        assertion_operator,
        assertion_expected,
        "Prefix message",
        message,
    )

AssertionEngine provides an interface to define scope for the formatters, but because scoping is a library-specific implementation, it is up to the library to decide how scoping is actually implemented. AssertionEngine Formatter class is an ABC which provides get_formatter and set_formatter interface methods for library developers. The AssertionEngine atest directory has examples how the interface can be implemented in practice: https://github.com/MarketSquare/AssertionEngine/tree/main/atest

For more information about Robot Framework see: http://robotframework.org For Browser library see: https://robotframework-browser.org/