Behavior-Driven Development for R.

cucumber

An implementation of the Cucumber testing framework in R. Fully native, no external dependencies.

Use it as an extension of your testthat tests or as a standalone testing stage.

Introduction

The package parses Gherkin documents

# tests/testthat/addition.feature
Feature: Addition
  Scenario: Adding 2 integers
    When I add 1 and 1
    Then the result is 2
  Scenario: Adding integer and float
    When I add 1 and 1.1
    Then the result is 2.1
  Scenario: Adding float and float
    When I add 1.1 and 1.1
    Then the result is 2.2

and uses step definitions to run the tests

# tests/testthat/steps/steps_definitions.R
when("I add {int} and {int}", function(x, y, context) {
  context$result <- x + y
})

then("the result is {int}", function(expected, context) {
  expect_equal(context$result, expected)
})

when("I add {int} and {float}", function(x, y, context) {
  context$result <- x + y
})

when("I add {float} and {float}", function(x, y, context) {
  context$result <- x + y
})

then("the result is {float}", function(expected, context) {
  expect_equal(context$result, expected)
})

Running cucumber tests with testthat tests.

To run cucumber as a part of testthat suite, create a test-cucumber.R file:

#' tests/testthat/test-cucumber.R
cucumber::test(".", "./steps")

When you run:

• testthat::test_dir("tests/testthat"),
• testthat::test_file("tests/testthat/test-cucumber.R"),
• or devtools::test(),

it will use the testthat reporter to show the results.

The building blocks of the cucumber tests are Features and Scenarios.

• Each Feature will be treated as a separate context – their results will be reported as if they were test-*.R files, e.g. 'test-Feature: Addition.R'.
• Each Scenario is equivalent to a testthat::test_that or testthat::it case. You get feedback on each Scenario separately. Only if all steps in a scenario are successful, the scenario is considered successful.

That means a succesful run for an Addition feature would produce the following output (with ProgressReporter).

| v | F W  S  OK | Context           |
| v | 3          | Feature: Addition |
== Results ================================================
[ FAIL 0 | WARN 0 | SKIP 0 | PASS 3 ]

And if it doesn't succeed, it will report which Scenarios failed in the Feature.

| v | F W  S  OK | Context           |
| x | 2        1 | Feature: Addition |
--------------------------------------------------------------------------------
Failure ('test-cucumber.R:1:1'): Scenario: Adding integer and float
context$result (`actual`) not equal to `expected` (`expected`).
`actual`: 2
`expected`: 5
Backtrace:
x
1. \-global `<step>`(expected = 5L, context = `<env>`)
2.   \-testthat::expect_equal(context$result, expected) at ./steps/addition.R:7:2
Failure ('test-cucumber.R:1:1'): Scenario: Adding float and float
context$result (`actual`) not equal to `expected` (`expected`).
`actual`: 2
`expected`: 5
Backtrace:
x
1. \-global `<step>`(expected = 5L, context = `<env>`)
2.   \-testthat::expect_equal(context$result, expected) at ./steps/addition.R:7:2
--------------------------------------------------------------------------------
== Results =====================================================================
-- Failed tests ----------------------------------------------------------------
Failure ('test-cucumber.R:1:1'): Scenario: Adding integer and float
context$result (`actual`) not equal to `expected` (`expected`).
`actual`: 2
`expected`: 5
Backtrace:
x
1. \-global `<step>`(expected = 5L, context = `<env>`)
2.   \-testthat::expect_equal(context$result, expected) at ./steps/addition.R:7:2
Failure ('test-cucumber.R:1:1'): Scenario: Adding float and float
context$result (`actual`) not equal to `expected` (`expected`).
`actual`: 2
`expected`: 5
Backtrace:
x
1. \-global `<step>`(expected = 5L, context = `<env>`)
2.   \-testthat::expect_equal(context$result, expected) at ./steps/addition.R:7:2
[ FAIL 1 | WARN 0 | SKIP 0 | PASS 2 ]

Running cucumber tests separately to unit tests

If you want to run cucumber tests separately, for example as a different testing step on CI, just put cucumber tests in other directory (or use testthat::test_dir filter parameter).

This may be especially useful, if cucumber tests are significantly slower than unit tests. It may often be the case as cucumber tests should target integration of different parts of the system and provide a high level confirmation if the system works as expected.

├── tests/
│   ├── cucumber/
│   │   ├── steps/
│   │   │   ├── feature_1_steps.R
│   │   │   ├── feature_2_steps.R
│   │   ├── feature_1.feature
│   │   ├── feature_2.feature
│   │   ├── test-cucumber.R
│   ├── testthat/
│   │   ├── test-unit_test_1.R
│   │   ├── test-unit_test_2.R

In that case you would run cucumber tests with testthat::test_dir("tests/cucumber").

Examples

See the examples directory to help you get started.

How it works

The .feature files are parsed and matched against step definitions.

Step functions are defined using:

• description: a cucumber expression.
• and an implementation function. It must have the parameters that will be matched in the description and a context parameter - an environment for managing state between steps.

If a step parsed from one of .feature files is not found, an error will be thrown.

Parameter types

Step implementations receive data from the .feature files as parameters. The values are detected via regular expressions and casted with a transformer function.

The following parameter types are available by default:

See cucumber::define_parameter_type() how to define your own parameter types.

Supported Gherkin syntax:

• [x] Feature
• [x] Scenario
• [x] Example
• [x] Given
• [x] When
• [x] Then
• [x] And
• [x] But
• [ ] Background
• [ ] Scenario Outline (or Scenario Template)
• [ ] Examples (or Scenarios)
• [x] """ (Doc Strings)
• [x] | (Data Tables)
• [ ] @ (Tags)
• [x] # (Comments)

See the Gherkin Reference on how to write Gherkin documents.

Installation

You can install the development version of cucumber from GitHub with:

devtools::install_github("jakubsob/cucumber")