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About Queries

Queries are the methods that the CLI Testing Library gives you to find processes in the command line. There are several types of queries ("get", "find", "query"); the difference between them is whether the query will throw an error if no CLI instance is found or if it will return a Promise and retry. Depending on what app content you are selecting, different queries may be more or less appropriate.

While our APIs differ slightly from upstream Testing Library's, their "About Queries" page summarizes the goals and intentions of this project's queries quite well.

Example

import {render} from 'cli-testing-library'

test('should show login form', () => {
  const {getByText} = render('ftp-automation.sh')
  const input = getByText('Username')
  // Events and assertions...
})

Types of Queries

  • getBy...: Returns the matching CLI instance for a query, and throw a descriptive error if no instances match.
  • queryBy...: Returns the matching CLI instance for a query, and return null if no instances match. This is useful for asserting an instance that is not present.
  • findBy...: Returns a Promise which resolves when a CLI instance is found which matches the given query. The promise is rejected if no instance is found after a default timeout of 1000ms.
Summary Table
Type of Query 0 Matches 1 Match >1 Matches Retry (Async/Await)
getBy... Throw error Return element Throw error No
queryBy... Return null Return element Throw error No
findBy... Throw error Return element Throw error Yes

TextMatch

Most of the query APIs take a TextMatch as an argument, which means the argument can be either a string, regex, or a function which returns true for a match and false for a mismatch.

TextMatch Examples

Given the following output string:

Hello World

Will find the instance:

// Matching a string:
getByText('Hello World') // full string match
getByText('llo Worl', {exact: false}) // substring match
getByText('hello world', {exact: false}) // ignore case

// Matching a regex:
getByText(/World/) // substring match
getByText(/world/i) // substring match, ignore case
getByText(/^hello world$/i) // full string match, ignore case
getByText(/Hello W?oRlD/i) // substring match, ignore case, searches for "hello world" or "hello orld"

// Matching with a custom function:
getByText((content, instance) => content.startsWith('Hello'))

Will not find the instance:

// full string does not match
getByText('Goodbye World')

// case-sensitive regex with different case
getByText(/hello world/)

// function looking contents that don't exist:
getByText((content, instance) => {
  return instance.stdoutStr.includes('Goodbye World')
})

Precision

Queries that take a TextMatch also accept an object as the final argument that can contain options that affect the precision of string matching:

  • exact: Defaults to true; matches full strings, case-sensitive. When false, matches substrings and is not case-sensitive.
    • exact has no effect on regex or function arguments.
    • In most cases using a regex instead of a string gives you more control over fuzzy matching and should be preferred over { exact: false }.
  • normalizer: An optional function which overrides normalization behavior. See Normalization.

Normalization

Before running any matching logic against text in stdout, CLI Testing Library automatically normalizes that text. By default, normalization consists of trimming whitespace from the start and end of text, collapsing multiple adjacent whitespace characters into a single space, and removing ANSI escapes.

If you want to prevent that normalization, or provide alternative normalization (e.g. to remove Unicode control characters), you can provide a normalizer function in the options object. This function will be given a string and is expected to return a normalized version of that string.

Note

Specifying a value for normalizer replaces the built-in normalization, but you can call getDefaultNormalizer to obtain a built-in normalizer, either to adjust that normalization or to call it from your own normalizer.

getDefaultNormalizer takes an options object which allows the selection of behaviour:

  • trim: Defaults to true. Trims leading and trailing whitespace
  • collapseWhitespace: Defaults to true. Collapses inner whitespace (newlines, tabs, repeated spaces) into a single space.
  • stripAnsi: Defaults to true. Removes ANSI escapes from stdout entirely to leave only human-readible text.

Normalization Examples

To perform a match against text without trimming:

getByText('text', {
  normalizer: getDefaultNormalizer({trim: false}),
})

To override normalization to remove some Unicode characters whilst keeping some (but not all) of the built-in normalization behavior:

getByText('text', {
  normalizer: str =>
    getDefaultNormalizer({trim: false})(str).replace(/[\u200E-\u200F]*/g, ''),
})

ByText

getByText, queryByText, findByText

API

getByText(
  // If you're using the return from `render`, then skip the container argument:
  instance: TestInstance,
  text: TextMatch,
  options?: {
    exact?: boolean = true,
    normalizer?: NormalizerFn,
  }): HTMLElement

This will search the instance to see if there's an stdout output matching the given TextMatch.

Input your name:
import {render} from 'cli-testing-library'

const {getByText} = render('command')
const instance = getByText(/input your name/i)

Options

Contains all of the TextMatch options

ByError

getByError, queryByError, findByError

API

getByText(
  // If you're using the return from `render`, then skip the container argument:
  instance: TestInstance,
  text: TextMatch,
  options?: {
    exact?: boolean = true,
    normalizer?: NormalizerFn,
  }): HTMLElement

This will search the instance to see if there's an stderr output matching the given TextMatch.

Could not find file
import {render} from 'cli-testing-library'

const {getByError} = render('command')
const instance = getByError(/not find file/)

Options

Contains all of the TextMatch options