diff --git a/packages/grafana-ui/src/themes/ThemeContext.test.tsx b/packages/grafana-ui/src/themes/ThemeContext.test.tsx index 26feb2c617c..e7ac00eef46 100644 --- a/packages/grafana-ui/src/themes/ThemeContext.test.tsx +++ b/packages/grafana-ui/src/themes/ThemeContext.test.tsx @@ -1,23 +1,69 @@ import React from 'react'; import { config } from '@grafana/runtime'; +import { renderHook } from '@testing-library/react-hooks'; import { css } from 'emotion'; import { mount } from 'enzyme'; -import { useStyles } from './ThemeContext'; +import { memoizedStyleCreators, mockThemeContext, useStyles } from './ThemeContext'; describe('useStyles', () => { - it('passes in theme and returns style object', () => { + it('memoizes the passed in function correctly', () => { + const stylesCreator = () => ({}); + const { rerender, result } = renderHook(() => useStyles(stylesCreator)); + const storedReference = result.current; + + rerender(); + expect(storedReference).toBe(result.current); + }); + + it('does not memoize if the passed in function changes every time', () => { + const { rerender, result } = renderHook(() => useStyles(() => ({}))); + const storedReference = result.current; + rerender(); + expect(storedReference).not.toBe(result.current); + }); + + it('updates the memoized function when the theme changes', () => { + const stylesCreator = () => ({}); + const { rerender, result } = renderHook(() => useStyles(stylesCreator)); + const storedReference = result.current; + + const restoreThemeContext = mockThemeContext({}); + rerender(); + expect(storedReference).not.toBe(result.current); + restoreThemeContext(); + }); + + it('cleans up memoized functions whenever a new one comes along or the component unmounts', () => { + const styleCreators: Function[] = []; + const { rerender, unmount } = renderHook(() => { + const styleCreator = () => ({}); + styleCreators.push(styleCreator); + return useStyles(styleCreator); + }); + + expect(typeof memoizedStyleCreators.get(styleCreators[0])).toBe('function'); + rerender(); + expect(memoizedStyleCreators.get(styleCreators[0])).toBeUndefined(); + expect(typeof memoizedStyleCreators.get(styleCreators[1])).toBe('function'); + unmount(); + expect(memoizedStyleCreators.get(styleCreators[0])).toBeUndefined(); + expect(memoizedStyleCreators.get(styleCreators[1])).toBeUndefined(); + }); + + it('passes in theme and returns style object', done => { const Dummy: React.FC = function() { const styles = useStyles(theme => { expect(theme).toEqual(config.theme); return { someStyle: css` - color: ${theme?.palette.critical}; + color: ${theme.palette.critical}; `, }; }); expect(typeof styles.someStyle).toBe('string'); + done(); return