feat: Support for regular expressions in toHaveClass (#563)

README.md

@@ -753,10 +753,12 @@ toHaveClass(...classNames: string[], options?: {exact: boolean})
 ```
 
 This allows you to check whether the given element has certain classes within
-its `class` attribute.
+its `class` attribute. You must provide at least one class, unless you are
+asserting that an element does not have any classes.
 
-You must provide at least one class, unless you are asserting that an element
-does not have any classes.
+The list of class names may include strings and regular expressions. Regular
+expressions are matched against each individual class in the target element, and
+it is NOT matched against its full `class` attribute value as whole.
 
 #### Examples
 
@@ -773,8 +775,11 @@ const noClasses = getByTestId('no-classes')
 
 expect(deleteButton).toHaveClass('extra')
 expect(deleteButton).toHaveClass('btn-danger btn')
+expect(deleteButton).toHaveClass(/danger/, 'btn')
 expect(deleteButton).toHaveClass('btn-danger', 'btn')
 expect(deleteButton).not.toHaveClass('btn-link')
+expect(deleteButton).not.toHaveClass(/link/)
+expect(deleteButton).not.toHaveClass(/btn extra/) // It does not match
 
 expect(deleteButton).toHaveClass('btn-danger extra btn', {exact: true}) // to check if the element has EXACTLY a set of classes
 expect(deleteButton).not.toHaveClass('btn-danger extra', {exact: true}) // if it has more than expected it is going to fail

src/__tests__/to-have-class.js

@@ -93,6 +93,32 @@ test('.toHaveClass', () => {
   ).toThrowError(/(none)/)
 })
 
+test('.toHaveClass with regular expressions', () => {
+  const {queryByTestId} = renderElementWithClasses()
+
+  expect(queryByTestId('delete-button')).toHaveClass(/btn/)
+  expect(queryByTestId('delete-button')).toHaveClass(/danger/)
+  expect(queryByTestId('delete-button')).toHaveClass(
+    /-danger$/,
+    'extra',
+    /^btn-[a-z]+$/,
+    /\bbtn/,
+  )
+
+  // It does not match with "btn extra", even though it is a substring of the
+  // class "btn extra btn-danger". This is because the regular expression is
+  // matched against each class individually.
+  expect(queryByTestId('delete-button')).not.toHaveClass(/btn extra/)
+
+  expect(() =>
+    expect(queryByTestId('delete-button')).not.toHaveClass(/danger/),
+  ).toThrowError()
+
+  expect(() =>
+    expect(queryByTestId('delete-button')).toHaveClass(/dangerous/),
+  ).toThrowError()
+})
+
 test('.toHaveClass with exact mode option', () => {
   const {queryByTestId} = renderElementWithClasses()
 
@@ -102,19 +128,21 @@ test('.toHaveClass with exact mode option', () => {
   expect(queryByTestId('delete-button')).not.toHaveClass('btn extra', {
     exact: true,
   })
-  expect(
-    queryByTestId('delete-button'),
-  ).not.toHaveClass('btn extra btn-danger foo', {exact: true})
+  expect(queryByTestId('delete-button')).not.toHaveClass(
+    'btn extra btn-danger foo',
+    {exact: true},
+  )
 
   expect(queryByTestId('delete-button')).toHaveClass('btn extra btn-danger', {
     exact: false,
   })
   expect(queryByTestId('delete-button')).toHaveClass('btn extra', {
     exact: false,
   })
-  expect(
-    queryByTestId('delete-button'),
-  ).not.toHaveClass('btn extra btn-danger foo', {exact: false})
+  expect(queryByTestId('delete-button')).not.toHaveClass(
+    'btn extra btn-danger foo',
+    {exact: false},
+  )
 
   expect(queryByTestId('delete-button')).toHaveClass(
     'btn',
@@ -178,3 +206,26 @@ test('.toHaveClass with exact mode option', () => {
     }),
   ).toThrowError(/Expected the element to have EXACTLY defined classes/)
 })
+
+test('.toHaveClass combining {exact:true} and regular expressions throws an error', () => {
+  const {queryByTestId} = renderElementWithClasses()
+
+  expect(() =>
+    expect(queryByTestId('delete-button')).not.toHaveClass(/btn/, {
+      exact: true,
+    }),
+  ).toThrowError()
+
+  expect(() =>
+    expect(queryByTestId('delete-button')).not.toHaveClass(
+      /-danger$/,
+      'extra',
+      /\bbtn/,
+      {exact: true},
+    ),
+  ).toThrowError()
+
+  expect(() =>
+    expect(queryByTestId('delete-button')).toHaveClass(/danger/, {exact: true}),
+  ).toThrowError()
+})

src/to-have-class.js

@@ -4,7 +4,7 @@ function getExpectedClassNamesAndOptions(params) {
   const lastParam = params.pop()
   let expectedClassNames, options
 
-  if (typeof lastParam === 'object') {
+  if (typeof lastParam === 'object' && !(lastParam instanceof RegExp)) {
     expectedClassNames = params
     options = lastParam
   } else {
@@ -15,14 +15,16 @@ function getExpectedClassNamesAndOptions(params) {
 }
 
 function splitClassNames(str) {
-  if (!str) {
-    return []
-  }
+  if (!str) return []
   return str.split(/\s+/).filter(s => s.length > 0)
 }
 
 function isSubset(subset, superset) {
-  return subset.every(item => superset.includes(item))
+  return subset.every(strOrRegexp =>
+    typeof strOrRegexp === 'string'
+      ? superset.includes(strOrRegexp)
+      : superset.some(className => strOrRegexp.test(className)),
+  )
 }
 
 export function toHaveClass(htmlElement, ...params) {
@@ -31,10 +33,20 @@ export function toHaveClass(htmlElement, ...params) {
 
   const received = splitClassNames(htmlElement.getAttribute('class'))
   const expected = expectedClassNames.reduce(
-    (acc, className) => acc.concat(splitClassNames(className)),
+    (acc, className) =>
+      acc.concat(
+        typeof className === 'string' || !className
+          ? splitClassNames(className)
+          : className,
+      ),
     [],
   )
 
+  const hasRegExp = expected.some(className => className instanceof RegExp)
+  if (options.exact && hasRegExp) {
+    throw new Error('Exact option does not support RegExp expected class names')
+  }
+
   if (options.exact) {
     return {
       pass: isSubset(expected, received) && expected.length === received.length,

types/__tests__/jest/jest-custom-expect-types.test.ts

@@ -38,7 +38,8 @@ customExpect(element).toHaveAttribute('attr', true)
 customExpect(element).toHaveAttribute('attr', 'yes')
 customExpect(element).toHaveClass()
 customExpect(element).toHaveClass('cls1')
-customExpect(element).toHaveClass('cls1', 'cls2', 'cls3', 'cls4')
+customExpect(element).toHaveClass(/cls/)
+customExpect(element).toHaveClass('cls1', 'cls2', /cls(3|4)/)
 customExpect(element).toHaveClass('cls1', {exact: true})
 customExpect(element).toHaveDisplayValue('str')
 customExpect(element).toHaveDisplayValue(['str1', 'str2'])
@@ -94,3 +95,6 @@ customExpect(element).toHaveErrorMessage(
 
 // @ts-expect-error The types accidentally allowed any property by falling back to "any"
 customExpect(element).nonExistentProperty()
+
+// @ts-expect-error
+customExpect(element).toHaveClass(/cls/, {exact: true})

types/matchers.d.ts

@@ -249,13 +249,14 @@ declare namespace matchers {
      * const noClasses = getByTestId('no-classes')
      * expect(deleteButton).toHaveClass('btn')
      * expect(deleteButton).toHaveClass('btn-danger xs')
+     * expect(deleteButton).toHaveClass(/danger/, 'xs')
      * expect(deleteButton).toHaveClass('btn xs btn-danger', {exact: true})
      * expect(deleteButton).not.toHaveClass('btn xs btn-danger', {exact: true})
      * expect(noClasses).not.toHaveClass()
      * @see
      * [testing-library/jest-dom#tohaveclass](https://github.com/testing-library/jest-dom#tohaveclass)
      */
-    toHaveClass(...classNames: string[]): R
+    toHaveClass(...classNames: Array<string | RegExp>): R
     toHaveClass(classNames: string, options?: {exact: boolean}): R
     /**
      * @description