API

Measurements

measureRenders() function

info

Prior to version 1.0, this function has been named measurePerformance.

Custom wrapper for the RNTL/RTL's render function responsible for rendering the passed screen inside a React.Profiler component, measuring its performance and writing results to the output file. You can use optional options object allows customizing aspects of the testing.

async function measureRenders(
  ui: React.ReactElement,
  options?: MeasureRendersOptions,
): Promise<MeasureResults> {

Example

// sample.perf-test.tsx
import { measureRenders } from 'reassure';
import { screen, fireEvent } from '@testing-library/react-native';
import { ComponentUnderTest } from './ComponentUnderTest';

test('Test with scenario', async () => {
  const scenario = async () => {
    fireEvent.press(screen.getByText('Go'));
    await screen.findByText('Done');
  };

  await measureRenders(<ComponentUnderTest />, { scenario });
});

MeasureRendersOptions type

interface MeasureRendersOptions {
  runs?: number;
  warmupRuns?: number;
  removeOutliers?: boolean;
  wrapper?: React.ComponentType<{ children: ReactElement }>;
  scenario?: (view?: RenderResult) => Promise<any>;
  writeFile?: boolean;
  beforeEach?: () => Promise<void> | void;
  afterEach?: () => Promise<void> | void;
}

• runs: number of runs per series for the particular test
• warmupRuns: number of additional warmup runs that will be done and discarded before the actual runs (default: 1)
• removeOutliers: should remove statistical outlier results (default: true)
• wrapper: React component, such as a Provider, which the ui will be wrapped with. Note: the render duration of the wrapper itself is excluded from the results, only the wrapped component is measured.
• scenario: a custom async function, which defines user interaction within the ui by utilized RNTL functions
• writeFile: should write output to file (default true)
• beforeEach: function to execute before each test run.
• afterEach: function to execute after each test run.

measureFunction function

Allows you to wrap any synchronous function, measure its performance and write results to the output file. You can use optional options to customize aspects of the testing.

async function measureFunction(
  fn: () => void,
  options?: MeasureFunctionOptions,
): Promise<MeasureResults> {

Example

// sample.perf-test.tsx
import { measureFunction } from 'reassure';
import { fib } from './fib';

test('fib 30', async () => {
  await measureFunction(() => fib(30));
});

MeasureFunctionOptions type

interface MeasureFunctionOptions {
  runs?: number;
  warmupRuns?: number;
  removeOutliers?: boolean;
  writeFile?: boolean;
  beforeEach?: () => Promise<void> | void;
  afterEach?: () => Promise<void> | void;
}

• runs: number of runs per series for the particular test
• warmupRuns: number of additional warmup runs that will be done and discarded before the actual runs
• removeOutliers: should remove statistical outlier results (default: true)
• writeFile: should write output to file (default true)
• beforeEach: function to execute before each test run.
• afterEach: function to execute after each test run.

measureAsyncFunction function

Allows you to wrap any asynchronous function, measure its performance and write results to the output file. You can use optional options to customize aspects of the testing.

info

Measuring performance of asynchronous functions can be tricky. These functions often depend on external conditions like I/O operations, network requests, or storage access, which introduce unpredictable timing variations in your measurements. For stable and meaningful performance metrics, always ensure all external calls are properly mocked in your test environment to avoid polluting your performance measurements with uncontrollable factors.

async function measureAsyncFunction(
  fn: () => Promise<unknown>,
  options?: MeasureAsyncFunctionOptions,
): Promise<MeasureResults> {

Example

// sample.perf-test.tsx
import { measureAsyncFunction } from 'reassure';
import { fib } from './fib';

test('fib 30', async () => {
  await measureAsyncFunction(async () => {
    return Promise.resolve().then(() => fib(30));
  });
});

MeasureAsyncFunctionOptions type

interface MeasureAsyncFunctionOptions {
  runs?: number;
  warmupRuns?: number;
  removeOutliers?: boolean;
  writeFile?: boolean;
  beforeEach?: () => Promise<void> | void;
  afterEach?: () => Promise<void> | void;
}

• runs: number of runs per series for the particular test
• warmupRuns: number of additional warmup runs that will be done and discarded before the actual runs
• removeOutliers: should remove statistical outlier results (default: true)
• writeFile: (default true) should write output to file
• beforeEach: function to execute before each test run.
• afterEach: function to execute after each test run.

Configuration

Default configuration

The default config which will be used by the measuring script. This configuration object can be overridden with the use of the configure function.

type Config = {
  runs?: number;
  warmupRuns?: number;
  outputFile?: string;
  verbose?: boolean;
  testingLibrary?:
    | 'react-native'
    | 'react'
    | { render: (component: React.ReactElement<any>) => any; cleanup: () => any };
};

const defaultConfig: Config = {
  runs: 10,
  warmupRuns: 1,
  outputFile: '.reassure/current.perf',
  verbose: false,
  testingLibrary: undefined, // Will try auto-detect first RNTL, then RTL
};

• runs: number of repeated runs in a series per test (allows for higher accuracy by aggregating more data). Should be handled with care.
• warmupRuns: number of additional warmup runs that will be done and discarded before the actual runs.
• outputFile: name of the file the records will be saved to
• verbose: make Reassure log more, e.g. for debugging purposes
• testingLibrary: where to look for render and cleanup functions, supported values 'react-native', 'react' or object providing custom render and cleanup functions

configure function

function configure(customConfig: Partial<Config>): void;

You can use the configure function to override the default config parameters.

Example

import { configure } from 'reassure';

configure({
  testingLibrary: 'react', // force using React Testing Library internally by Reassure to render and cleanup
  runs: 7, // by default repeat performance tests 7 times
});

resetToDefaults function

resetToDefaults(): void

Reset current config to the original defaultConfig object. You can call resetToDefaults() anywhere in your performance test file.

Environmental variables

The reassure CLI can be parametrized using available environmental variables:

• TEST_RUNNER_PATH: an alternative path for your test runner. Defaults to 'node_modules/.bin/jest' or on Windows 'node_modules/jest/bin/jest'
• TEST_RUNNER_ARGS: a set of arguments fed to the runner. Defaults to '--runInBand --testMatch "**/__perf__/**/*.[jt]s?(x)", "**/*.(perf|perf-test).[jt]s?(x)"

Example:

TEST_RUNNER_PATH=myOwnPath/jest/bin yarn reassure