Cucumber Expressions

Cucumber Expressions are simple patterns for matching Step Definitions with Gherkin steps.

Implementation status

Cucumber Expressions provide an alternative to Regular Expressions which is easier to read and write for humans.

This is an example of a Cucumber expression with a single argument {n}:

I have {n} cukes in my belly

This expression would match the following Gherkin step text (The Given keyword has been removed):

I have 42 cukes in my belly

When this step is matched against the expression, the {n} argument would get the value "22" and be passed to the step definition's body.

Type transformations

Cucumber Expressions have built-in support for transformation of arguments to arbitrary types.

Expression types

The type of an argument can be specified within the expression:

I have {n:int} cukes in my belly

In this case the argument would get the value 42 (an integer) instead of "42" (a string).

The types you can specify in Cucumber Expressions are int and float, and any additional numeric types available in your programming language.

Explicit types

In statically typed programming languages the argument types can be derived from the step definition body's parameters. Here is an example in Java:

Given("I have {n} cukes in my belly", (int n) -> {
})

Custom type transforms

You can also register your own types:

Cucumber.addTransform(new FunctionTransform<>(
  Currency.class,
  "[A-Z]{3}",
  Currency::parse
));