Improved reliability of snapshots by having consistent order of extracted rules (#1880)

* Fix inconsistent style ordering for snapshots

Due to jest writing styles in the order it encounters
rendered styled components across tests, an issue can
occur where skipping/removing/reordering your tests will
invalidate test snapshots.

This fix sorts the style elements when serializing emotion styles.

* Add changeset for @jest/emotion style sorting

* update snapshots for style reordering fix

* Rewrite style extraction in the serializer to be independent of the rules insertion order

Co-authored-by: Mateusz Burzyński <[email protected]>

Author: Jimmydalecleveland

.changeset/fresh-clouds-tell.md

@@ -0,0 +1,5 @@
+---
+'@emotion/jest': patch
+---
+
+Improved stability of the generated snapshots - styles are extracted now based on the order in which the associated with them class names appear in the serialized elements rather than based on the order of the actual rules in the document.

packages/css/test/__snapshots__/component-selector.test.js.snap

@@ -1,19 +1,19 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`component selector should be converted to use the emotion target className 1`] = `
-.emotion-0 {
-  color: blue;
+.emotion-0 .emotion-2 {
+  color: red;
 }
 
-.emotion-2 .emotion-1 {
-  color: red;
+.emotion-1 {
+  color: blue;
 }
 
 <div
-  className="emotion-2"
+  className="emotion-0"
 >
   <div
-    className="emotion-0 emotion-1"
+    className="emotion-1 emotion-2"
   />
 </div>
 `;

packages/css/test/__snapshots__/css.test.js.snap

@@ -439,38 +439,6 @@ exports[`css nested at rule 1`] = `
 />
 `;
 
-exports[`css nested at rules 1`] = `
-@media (min-width: 420px) {
-  .glamor-0 {
-    color: pink;
-  }
-}
-
-@media (min-width: 420px) and  (max-width: 500px) {
-  .glamor-0 {
-    color: hotpink;
-  }
-}
-
-@supports (display: grid) {
-  .glamor-0 {
-    display: grid;
-  }
-}
-
-@supports (display: grid) and  ((display: -webkit-box) or (display: flex)) {
-  .glamor-0 {
-    display: -webkit-box;
-    display: -ms-flexbox;
-    display: flex;
-  }
-}
-
-<div
-  className="glamor-0"
-/>
-`;
-
 exports[`css null rule 1`] = `
 <div
   className="emotion-0"

packages/jest/src/create-serializer.js

@@ -23,16 +23,16 @@ function getNodes(node, nodes = []) {
     return nodes
   }
 
+  if (typeof node === 'object') {
+    nodes.push(node)
+  }
+
   if (node.children) {
     for (let child of node.children) {
       getNodes(child, nodes)
     }
   }
 
-  if (typeof node === 'object') {
-    nodes.push(node)
-  }
-
   return nodes
 }
 

packages/jest/src/utils.js

@@ -18,6 +18,20 @@ export function findLast<T>(arr: T[], predicate: T => boolean) {
   }
 }
 
+export function findIndexFrom<T>(
+  arr: T[],
+  fromIndex: number,
+  predicate: T => boolean
+) {
+  for (let i = fromIndex; i < arr.length; i++) {
+    if (predicate(arr[i])) {
+      return i
+    }
+  }
+
+  return -1
+}
+
 function getClassNames(selectors: any, classes?: string) {
   return classes ? selectors.concat(classes.split(' ')) : selectors
 }
@@ -128,6 +142,19 @@ const getElementRules = (element: HTMLStyleElement): string[] => {
   return [].slice.call(element.sheet.cssRules).map(cssRule => cssRule.cssText)
 }
 
+const getKeyframesMap = rules =>
+  rules.reduce((keyframes, rule) => {
+    const match = rule.match(keyframesPattern)
+    if (match !== null) {
+      const name = match[1]
+      if (keyframes[name] === undefined) {
+        keyframes[name] = ''
+      }
+      keyframes[name] += rule
+    }
+    return keyframes
+  }, {})
+
 export function getStylesFromClassNames(
   classNames: Array<string>,
   elements: Array<HTMLStyleElement>
@@ -155,25 +182,36 @@ export function getStylesFromClassNames(
     return ''
   }
   const selectorPattern = new RegExp(
-    '\\.(' + filteredClassNames.join('|') + ')'
+    '\\.(?:' + filteredClassNames.map(cls => `(${cls})`).join('|') + ')'
   )
-  const keyframes = {}
-  let styles = ''
 
-  flatMap(elements, getElementRules).forEach((rule: string) => {
-    if (selectorPattern.test(rule)) {
-      styles += rule
-    }
-    const match = rule.match(keyframesPattern)
-    if (match !== null) {
-      const name = match[1]
-      if (keyframes[name] === undefined) {
-        keyframes[name] = ''
+  const rules = flatMap(elements, getElementRules)
+
+  let styles = rules
+    .map((rule: string) => {
+      const match = rule.match(selectorPattern)
+      if (!match) {
+        return null
       }
-      keyframes[name] += rule
-    }
-  })
-  const keyframeNameKeys = Object.keys(keyframes)
+      // `selectorPattern` represents all emotion-generated class names
+      // each possible class name is wrapped in a capturing group
+      // and those groups appear in the same order as they appear in the DOM within class attributes
+      // because we've gathered them from the DOM in such order
+      // given that information we can sort matched rules based on the capturing group that has been matched
+      // to end up with styles in a stable order
+      const matchedCapturingGroupIndex = findIndexFrom(match, 1, Boolean)
+      return [rule, matchedCapturingGroupIndex]
+    })
+    .filter(Boolean)
+    .sort(
+      ([ruleA, classNameIndexA], [ruleB, classNameIndexB]) =>
+        classNameIndexA - classNameIndexB
+    )
+    .map(([rule]) => rule)
+    .join('')
+
+  const keyframesMap = getKeyframesMap(rules)
+  const keyframeNameKeys = Object.keys(keyframesMap)
   let keyframesStyles = ''
 
   if (keyframeNameKeys.length) {
@@ -184,7 +222,7 @@ export function getStylesFromClassNames(
     styles = styles.replace(keyframesNamePattern, name => {
       if (keyframesNameCache[name] === undefined) {
         keyframesNameCache[name] = `animation-${index++}`
-        keyframesStyles += keyframes[name]
+        keyframesStyles += keyframesMap[name]
       }
       return keyframesNameCache[name]
     })

packages/jest/test/__snapshots__/preact.test.js.snap

@@ -3,19 +3,19 @@
 exports[`jest-emotion with preact handles elements with no props 1`] = `"<div />"`;
 
 exports[`jest-emotion with preact replaces class names and inserts styles into preact test component snapshots 1`] = `
-".emotion-1 {
+".emotion-0 {
   color: red;
 }
 
-.emotion-0 {
+.emotion-1 {
   width: 100%;
 }
 
 <div
-  class=\\"emotion-1\\"
+  class=\\"emotion-0\\"
 >
   <svg
-    class=\\"emotion-0\\"
+    class=\\"emotion-1\\"
   />
 </div>"
 `;

packages/jest/test/__snapshots__/printer.test.js.snap

@@ -21,55 +21,55 @@ exports[`jest-emotion with DOM elements disabled does not replace class names or
 `;
 
 exports[`jest-emotion with DOM elements disabled replaces class names and inserts styles into React test component snapshots 1`] = `
-".emotion-1 {
+".emotion-0 {
   color: red;
 }
 
-.emotion-0 {
+.emotion-1 {
   width: 100%;
 }
 
 <div
-  className=\\"emotion-1\\"
+  className=\\"emotion-0\\"
 >
   <svg
-    className=\\"emotion-0\\"
+    className=\\"emotion-1\\"
   />
 </div>"
 `;
 
 exports[`jest-emotion with dom elements replaces class names and inserts styles into DOM element snapshots 1`] = `
-".emotion-1 {
+".emotion-0 {
   color: red;
 }
 
-.emotion-0 {
+.emotion-1 {
   width: 100%;
 }
 
 <div
-  class=\\"emotion-1\\"
+  class=\\"emotion-0\\"
 >
   <svg
-    class=\\"emotion-0\\"
+    class=\\"emotion-1\\"
   />
 </div>"
 `;
 
 exports[`jest-emotion with dom elements replaces class names and inserts styles into React test component snapshots 1`] = `
-".emotion-1 {
+".emotion-0 {
   color: red;
 }
 
-.emotion-0 {
+.emotion-1 {
   width: 100%;
 }
 
 <div
-  className=\\"emotion-1\\"
+  className=\\"emotion-0\\"
 >
   <svg
-    className=\\"emotion-0\\"
+    className=\\"emotion-1\\"
   />
 </div>"
 `;

packages/react/__tests__/__snapshots__/use-theme.js.snap

@@ -1,28 +1,28 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`Nested useTheme works 1`] = `
-.emotion-1 {
+.emotion-0 {
   color: green;
 }
 
-.emotion-1:hover {
+.emotion-0:hover {
   color: darkgreen;
 }
 
-.emotion-0 {
+.emotion-1 {
   color: lawngreen;
 }
 
-.emotion-0:hover {
+.emotion-1:hover {
   color: seagreen;
 }
 
 <div
-  className="emotion-1"
+  className="emotion-0"
 >
   Should be green
   <div
-    className="emotion-0"
+    className="emotion-1"
   >
     Should be lawngreen
   </div>

packages/styled/__tests__/__snapshots__/styled.js.snap

@@ -45,22 +45,22 @@ exports[`styled call expression 1`] = `
 
 exports[`styled component selectors 1`] = `
 .emotion-0 {
-  color: hotpink;
-}
-
-.emotion-2 {
   color: green;
 }
 
-.emotion-2 .emotion-1 {
+.emotion-0 .emotion-2 {
   color: yellow;
 }
 
+.emotion-1 {
+  color: hotpink;
+}
+
 <div
-  className="emotion-2"
+  className="emotion-0"
 >
   <div
-    className="emotion-0 emotion-1"
+    className="emotion-1 emotion-2"
   />
 </div>
 `;
@@ -329,30 +329,30 @@ exports[`styled keyframes with css call 1`] = `
 
 exports[`styled nested 1`] = `
 .emotion-0 {
-  font-size: 20px;
-}
-
-.emotion-1 {
   display: -webkit-box;
   display: -webkit-flex;
   display: -ms-flexbox;
   display: flex;
 }
 
-.emotion-1 div {
+.emotion-0 div {
   color: green;
 }
 
-.emotion-1 div span {
+.emotion-0 div span {
   color: red;
 }
 
+.emotion-1 {
+  font-size: 20px;
+}
+
 <div
-  className="emotion-1"
+  className="emotion-0"
 >
   hello 
   <h1
-    className="emotion-0"
+    className="emotion-1"
   >
     This will be green
   </h1>