describe {testthat} | R Documentation

## describe: a BDD testing language

### Description

A simple BDD DSL for writing tests. The language is similiar to RSpec for Ruby or Mocha for JavaScript. BDD tests read like sentences and it should thus be easier to understand what the specification of a function/component is.

### Usage

    describe(description, code)

### Arguments

`description` | description of the feature
`code` | test code containing the specs

### Details

Tests using the `describe` syntax not only verify the tested code, but also document its intended behaviour. Each `describe` block specifies a larger component or function and contains a set of specifications. A specification is definied by an `it` block. Each `it` block functions as a test and is evaluated in its own environment. You can also have nested `describe` blocks.

This test syntax helps to test the intented behaviour of your code. For example: you want to write a new function for your package. Try to describe the specification first using `describe`, before your write any code. After that, you start to implement the tests for each specification (i.e. the `it` block).

Use `describe` to verify that you implement the right things and use `test_that()` to ensure you do the things right.

### Examples

    describe("matrix()", {
      it("can be multiplied by a scalar", {
        m1 <- matrix(1:4, 2, 2)
        m2 <- m1 * 2
        expect_equivalent(matrix(1:4 * 2, 2, 2), m2)
      })
      it("can have not yet tested specs")
    })

    # Nested specs:
    ## code
    addition <- function(a, b) a + b
    division <- function(a, b) a / b

    ## specs
    describe("math library", {
      describe("addition()", {
        it("can add two numbers", {
          expect_equivalent(1 + 1, addition(1, 1))
        })
      })
      describe("division()", {
        it("can divide two numbers", {
          expect_equivalent(10 / 2, division(10, 2))
        })
        it("can handle division by 0") #not yet implemented
      })
    })

[Package testthat version 2.1.1 Index]