feat: support snapshot matching in node:test implementation

package.json

@@ -64,6 +64,7 @@
     "src/engine.js",
     "src/engine.node.cjs",
     "src/engine.pure.cjs",
+    "src/engine.pure.snapshot.cjs",
     "src/engine.select.cjs",
     "src/jest.js",
     "src/jest.config.js",

src/engine.pure.cjs

@@ -1,5 +1,6 @@
 const assert = require('node:assert/strict')
 const assertLoose = require('node:assert')
+const { matchSnapshot } = require('./engine.pure.snapshot.cjs')
 
 const { setTimeout, setInterval, setImmediate, Date } = globalThis
 const { clearTimeout, clearInterval, clearImmediate } = globalThis
@@ -28,17 +29,21 @@ class Context {
   children = []
   assert = { ...assertLoose, snapshot: undefined }
   hooks = { __proto__: null, before: [], after: [], beforeEach: [], afterEach: [] }
+  #fullName
 
   constructor(parent, name, options = {}) {
     Object.assign(this, { root: parent?.root, parent, name, options })
-    this.fullName = parent && parent !== parent.root ? `${parent.fullName} > ${name}` : name
-    if (this.fullName === name) this.fullName = this.fullName.replace(INBAND_PREFIX_REGEX, '')
+    this.#fullName = parent && parent !== parent.root ? `${parent.fullName} > ${name}` : name
+    if (this.#fullName === name) this.#fullName = this.#fullName.replace(INBAND_PREFIX_REGEX, '')
     if (this.root) {
       this.parent.children.push(this)
     } else {
       assert(this.name === '<root>' && !this.parent)
       this.root = this
     }
+
+    this.assert.snapshot = (obj) =>
+      matchSnapshot(readSnapshot, assert, this.fullName, serializeSnapshot(obj))
   }
 
   get onlySomewhere() {
@@ -48,6 +53,10 @@ class Context {
   get only() {
     return (this.options.only && !this.children.some((x) => x.onlySomewhere)) || this.parent?.only
   }
+
+  get fullName() {
+    return this.#fullName
+  }
 }
 
 function enterContext(name, options) {
@@ -466,7 +475,17 @@ if (process.env.EXODUS_TEST_ENVIRONMENT === 'bundle') {
 
 // eslint-disable-next-line no-undef
 let snapshotResolver = (dir, name) => [dir, `${name}.snapshot`] // default per Node.js docs
-const setSnapshotSerializers = () => {}
+let snapshotSerializers = [(obj) => JSON.stringify(obj, null, 2)]
+const serializeSnapshot = (obj) => {
+  let val = obj
+  for (const fn of snapshotSerializers) val = fn(val)
+  return val
+}
+
+const setSnapshotSerializers = ([...arr]) => {
+  snapshotSerializers = arr
+}
+
 const setSnapshotResolver = (fn) => {
   snapshotResolver = fn
 }

src/engine.pure.snapshot.cjs

@@ -0,0 +1,35 @@
+const nameCounts = new Map()
+let snapshotText
+
+const escapeSnapshot = (str) => str.replaceAll(/([\\`])/gu, '\\$1')
+
+function matchSnapshot(readSnapshot, assert, name, serialized) {
+  // We don't have native snapshots, polyfill reading
+  if (snapshotText !== null) {
+    try {
+      const snapshotRaw = readSnapshot()
+      snapshotText = snapshotRaw ? `\n${snapshotRaw}\n` : null // we'll search wrapped in \n
+    } catch {
+      snapshotText = null
+    }
+  }
+
+  const addFail = `Adding new snapshots requires Node.js >=22.3.0`
+
+  // We don't support polyfilled snapshot generation here, only parsing
+  // Also be careful with assertion plan counters
+  if (!snapshotText) assert.fail(`Could not find snapshot file. ${addFail}`)
+
+  const count = (nameCounts.get(name) || 0) + 1
+  nameCounts.set(name, count)
+  const escaped = escapeSnapshot(serialized)
+  const key = `${name} ${count}`
+  const makeEntry = (x) => `\nexports[\`${escapeSnapshot(key)}\`] = \`${x}\`;\n`
+  const final = escaped.includes('\n') ? `\n${escaped}\n` : escaped
+  if (snapshotText.includes(makeEntry(final))) return
+  // Perhaps wrapped with newlines from Node.js snapshots?
+  if (!final.includes('\n') && snapshotText.includes(makeEntry(`\n${final}\n`))) return
+  return assert.fail(`Could not match "${key}" in snapshot. ${addFail}`)
+}
+
+module.exports = { escapeSnapshot, matchSnapshot }

src/jest.snapshot.js

@@ -11,6 +11,7 @@ import { format, plugins as builtinPlugins } from 'pretty-format'
 import { jestConfig } from './jest.config.js'
 import { getTestNamePath } from './dark.cjs'
 import { haveSnapshotsReportUnescaped } from './version.js'
+import { matchSnapshot, escapeSnapshot } from './engine.pure.snapshot.cjs'
 
 const { snapshotFormat, snapshotSerializers } = jestConfig()
 const plugins = Object.values(builtinPlugins)
@@ -19,10 +20,6 @@ const serialize = (val) => format(val, { ...snapshotFormat, plugins }).replaceAl
 let serializersAreSetup = false
 let snapshotsAreJest = false
 
-// For manually loading the snapshot
-const nameCounts = new Map()
-let snapshotText
-
 function maybeSetupSerializers() {
   if (serializersAreSetup) return
   // empty require and serializers should not let this fail, non-empty serializers and empty require should
@@ -124,47 +121,20 @@ const snapOnDisk = (orig, matcher) => {
   }
 
   const obj = matcher ? deepMerge(orig, matcher) : orig
-  const escape = (str) => str.replaceAll(/([\\`])/gu, '\\$1')
 
   maybeSetupJestSnapshots()
 
   if (!context?.assert?.snapshot) {
-    // We don't have native snapshots, polyfill reading
-    if (snapshotText !== null) {
-      try {
-        const snapshotRaw = readSnapshot()
-        snapshotText = snapshotRaw ? `\n${snapshotRaw}\n` : null // we'll search wrapped in \n
-      } catch {
-        snapshotText = null
-      }
-    }
-
-    const addFail = `Adding new snapshots requires Node.js >=22.3.0`
-
-    // We don't support polyfilled snapshot generation here, only parsing
-    // Also be careful with assertion plan counters
-    if (!snapshotText) getAssert().fail(`Could not find snapshot file. ${addFail}`)
-
     const namePath = getTestNamePath(context).map((x) => (x === '<anonymous>' ? '' : x))
-    const name = namePath.join(' ')
-    const count = (nameCounts.get(name) || 0) + 1
-    nameCounts.set(name, count)
-    const escaped = escape(serialize(obj))
-    const key = `${name} ${count}`
-    const makeEntry = (x) => `\nexports[\`${escape(key)}\`] = \`${x}\`;\n`
-    const final = escaped.includes('\n') ? `\n${escaped}\n` : escaped
-    if (snapshotText.includes(makeEntry(final))) return
-    // Perhaps wrapped with newlines from Node.js snapshots?
-    if (!final.includes('\n') && snapshotText.includes(makeEntry(`\n${final}\n`))) return
-    return getAssert().fail(`Could not match "${key}" in snapshot. ${addFail}`)
+    return matchSnapshot(readSnapshot, getAssert(), namePath.join(' '), serialize(obj))
   }
 
   // Node.js always wraps with newlines, while jest wraps only those that are already multiline
   try {
     wrapContextName(() => context.assert.snapshot(obj))
   } catch (e) {
     if (typeof e.expected === 'string') {
-      const escaped = haveSnapshotsReportUnescaped ? e.expected : escape(e.expected)
+      const escaped = haveSnapshotsReportUnescaped ? e.expected : escapeSnapshot(e.expected)
       const final = escaped.includes('\n') ? escaped : `\n${escaped}\n`
       if (final === e.actual) return
     }