Upgrade Ava to v4

node_modules/ava/lib/snapshot-manager.js

@@ -1,24 +1,24 @@
-'use strict';
+import {Buffer} from 'node:buffer';
+import crypto from 'node:crypto';
+import fs from 'node:fs';
+import {findSourceMap} from 'node:module';
+import path from 'node:path';
+import {fileURLToPath} from 'node:url';
+import zlib from 'node:zlib';
 
-const crypto = require('crypto');
-const fs = require('fs');
-const path = require('path');
-const zlib = require('zlib');
+import cbor from 'cbor';
+import concordance from 'concordance';
+import indentString from 'indent-string';
+import mem from 'mem';
+import slash from 'slash';
+import writeFileAtomic from 'write-file-atomic';
 
-const concordance = require('concordance');
-const indentString = require('indent-string');
-const md5Hex = require('md5-hex');
-const convertSourceMap = require('convert-source-map');
-const slash = require('slash');
-const writeFileAtomic = require('write-file-atomic');
-const mem = require('mem');
-
-const concordanceOptions = require('./concordance-options').snapshotManager;
+import {snapshotManager as concordanceOptions} from './concordance-options.js';
 
 // Increment if encoding layout or Concordance serialization versions change. Previous AVA versions will not be able to
 // decode buffers generated by a newer version, so changing this value will require a major version bump of AVA itself.
 // The version is encoded as an unsigned 16 bit integer.
-const VERSION = 2;
+const VERSION = 3;
 
 const VERSION_HEADER = Buffer.alloc(2);
 VERSION_HEADER.writeUInt16LE(VERSION);
@@ -28,26 +28,24 @@ const READABLE_PREFIX = Buffer.from(`AVA Snapshot v${VERSION}\n`, 'ascii');
 const REPORT_SEPARATOR = Buffer.from('\n\n', 'ascii');
 const REPORT_TRAILING_NEWLINE = Buffer.from('\n', 'ascii');
 
-const MD5_HASH_LENGTH = 16;
+const SHA_256_HASH_LENGTH = 32;
 
-class SnapshotError extends Error {
+export class SnapshotError extends Error {
 	constructor(message, snapPath) {
 		super(message);
 		this.name = 'SnapshotError';
 		this.snapPath = snapPath;
 	}
 }
-exports.SnapshotError = SnapshotError;
 
-class ChecksumError extends SnapshotError {
+export class ChecksumError extends SnapshotError {
 	constructor(snapPath) {
 		super('Checksum mismatch', snapPath);
 		this.name = 'ChecksumError';
 	}
 }
-exports.ChecksumError = ChecksumError;
 
-class VersionMismatchError extends SnapshotError {
+export class VersionMismatchError extends SnapshotError {
 	constructor(snapPath, version) {
 		super('Unexpected snapshot version', snapPath);
 		this.name = 'VersionMismatchError';
@@ -55,20 +53,25 @@ class VersionMismatchError extends SnapshotError {
 		this.expectedVersion = VERSION;
 	}
 }
-exports.VersionMismatchError = VersionMismatchError;
+
+export class InvalidSnapshotError extends SnapshotError {
+	constructor(snapPath) {
+		super('Invalid snapshot file', snapPath);
+		this.name = 'InvalidSnapshotError';
+	}
+}
 
 const LEGACY_SNAPSHOT_HEADER = Buffer.from('// Jest Snapshot v1');
 function isLegacySnapshot(buffer) {
 	return LEGACY_SNAPSHOT_HEADER.equals(buffer.slice(0, LEGACY_SNAPSHOT_HEADER.byteLength));
 }
 
-class LegacyError extends SnapshotError {
+export class LegacyError extends SnapshotError {
 	constructor(snapPath) {
 		super('Legacy snapshot file', snapPath);
 		this.name = 'LegacyError';
 	}
 }
-exports.LegacyError = LegacyError;
 
 function tryRead(file) {
 	try {
@@ -82,168 +85,117 @@ function tryRead(file) {
 	}
 }
 
-function withoutLineEndings(buffer) {
-	let checkPosition = buffer.byteLength - 1;
-	while (buffer[checkPosition] === 0x0A || buffer[checkPosition] === 0x0D) {
-		checkPosition--;
-	}
+function formatEntry(snapshot, index) {
+	const {
+		data,
+		label = `Snapshot ${index + 1}`, // Human-readable labels start counting at 1.
+	} = snapshot;
 
-	return buffer.slice(0, checkPosition + 1);
+	const description = data
+		? concordance.formatDescriptor(concordance.deserialize(data), concordanceOptions)
+		: '<No Data>';
+
+	const blockquote = label.split(/\n/).map(line => '> ' + line).join('\n');
+
+	return `${blockquote}\n\n${indentString(description, 4)}`;
 }
 
-function formatEntry(label, descriptor) {
-	if (label) {
-		label = `> ${label}\n\n`;
-	}
+function combineEntries({blocks}) {
+	const combined = new BufferBuilder();
 
-	const codeBlock = indentString(concordance.formatDescriptor(descriptor, concordanceOptions), 4);
-	return Buffer.from(label + codeBlock, 'utf8');
-}
+	for (const {title, snapshots} of blocks) {
+		const last = snapshots[snapshots.length - 1];
+		combined.write(`\n\n## ${title}\n\n`);
 
-function combineEntries(entries) {
-	const buffers = [];
-	let byteLength = 0;
+		for (const [index, snapshot] of snapshots.entries()) {
+			combined.write(formatEntry(snapshot, index));
 
-	const sortedKeys = [...entries.keys()].sort((keyA, keyB) => {
-		const [a, b] = [entries.get(keyA), entries.get(keyB)];
-		const taskDifference = a.taskIndex - b.taskIndex;
-
-		if (taskDifference !== 0) {
-			return taskDifference;
-		}
-
-		const [assocA, assocB] = [a.associatedTaskIndex, b.associatedTaskIndex];
-		if (assocA !== undefined && assocB !== undefined) {
-			const assocDifference = assocA - assocB;
-
-			if (assocDifference !== 0) {
-				return assocDifference;
-			}
-		}
-
-		return a.snapIndex - b.snapIndex;
-	});
-
-	for (const key of sortedKeys) {
-		const keyBuffer = Buffer.from(`\n\n## ${key}\n\n`, 'utf8');
-		buffers.push(keyBuffer);
-		byteLength += keyBuffer.byteLength;
-
-		const formattedEntries = entries.get(key).buffers;
-		const last = formattedEntries[formattedEntries.length - 1];
-		for (const entry of formattedEntries) {
-			buffers.push(entry);
-			byteLength += entry.byteLength;
-
-			if (entry !== last) {
-				buffers.push(REPORT_SEPARATOR);
-				byteLength += REPORT_SEPARATOR.byteLength;
+			if (snapshot !== last) {
+				combined.write(REPORT_SEPARATOR);
 			}
 		}
 	}
 
-	return {buffers, byteLength};
+	return combined;
 }
 
-function generateReport(relFile, snapFile, entries) {
-	const combined = combineEntries(entries);
-	const {buffers} = combined;
-	let {byteLength} = combined;
-
-	const header = Buffer.from(`# Snapshot report for \`${slash(relFile)}\`
+function generateReport(relFile, snapFile, snapshots) {
+	return new BufferBuilder()
+		.write(`# Snapshot report for \`${slash(relFile)}\`
 
 The actual snapshot is saved in \`${snapFile}\`.
 
-Generated by [AVA](https://avajs.dev).`, 'utf8');
-	buffers.unshift(header);
-	byteLength += header.byteLength;
-
-	buffers.push(REPORT_TRAILING_NEWLINE);
-	byteLength += REPORT_TRAILING_NEWLINE.byteLength;
-	return Buffer.concat(buffers, byteLength);
+Generated by [AVA](https://avajs.dev).`)
+		.append(combineEntries(snapshots))
+		.write(REPORT_TRAILING_NEWLINE)
+		.toBuffer();
 }
 
-function appendReportEntries(existingReport, entries) {
-	const combined = combineEntries(entries);
-	const {buffers} = combined;
-	let {byteLength} = combined;
+class BufferBuilder {
+	constructor() {
+		this.buffers = [];
+		this.byteOffset = 0;
+	}
 
-	const prepend = withoutLineEndings(existingReport);
-	buffers.unshift(prepend);
-	byteLength += prepend.byteLength;
+	append(builder) {
+		this.buffers.push(...builder.buffers);
+		this.byteOffset += builder.byteOffset;
+		return this;
+	}
 
-	buffers.push(REPORT_TRAILING_NEWLINE);
-	byteLength += REPORT_TRAILING_NEWLINE.byteLength;
-	return Buffer.concat(buffers, byteLength);
-}
-
-function encodeSnapshots(buffersByHash) {
-	const buffers = [];
-	let byteOffset = 0;
-
-	// Entry start and end pointers are relative to the header length. This means
-	// it's possible to append new entries to an existing snapshot file, without
-	// having to rewrite pointers for existing entries.
-	const headerLength = Buffer.alloc(4);
-	buffers.push(headerLength);
-	byteOffset += 4;
-
-	// Allows 65535 hashes (tests or identified snapshots) per file.
-	const numberHashes = Buffer.alloc(2);
-	numberHashes.writeUInt16LE(buffersByHash.size);
-	buffers.push(numberHashes);
-	byteOffset += 2;
-
-	const entries = [];
-	// Maps can't have duplicate keys, so all items in [...buffersByHash.keys()]
-	// are unique, so sortedHashes should be deterministic.
-	const sortedHashes = [...buffersByHash.keys()].sort();
-	const sortedBuffersByHash = [...sortedHashes.map(hash => [hash, buffersByHash.get(hash)])];
-	for (const [hash, snapshotBuffers] of sortedBuffersByHash) {
-		buffers.push(Buffer.from(hash, 'hex'));
-		byteOffset += MD5_HASH_LENGTH;
-
-		// Allows 65535 snapshots per hash.
-		const numberSnapshots = Buffer.alloc(2);
-		numberSnapshots.writeUInt16LE(snapshotBuffers.length, 0);
-		buffers.push(numberSnapshots);
-		byteOffset += 2;
-
-		for (const value of snapshotBuffers) {
-			// Each pointer is 32 bits, restricting the total, uncompressed buffer to
-			// 4 GiB.
-			const start = Buffer.alloc(4);
-			const end = Buffer.alloc(4);
-			entries.push({start, end, value});
-
-			buffers.push(start, end);
-			byteOffset += 8;
+	write(data) {
+		if (typeof data === 'string') {
+			this.write(Buffer.from(data, 'utf8'));
+		} else {
+			this.buffers.push(data);
+			this.byteOffset += data.byteLength;
 		}
+
+		return this;
 	}
 
-	headerLength.writeUInt32LE(byteOffset, 0);
-
-	let bodyOffset = 0;
-	for (const entry of entries) {
-		const start = bodyOffset;
-		const end = bodyOffset + entry.value.byteLength;
-		entry.start.writeUInt32LE(start, 0);
-		entry.end.writeUInt32LE(end, 0);
-		buffers.push(entry.value);
-		bodyOffset = end;
+	toBuffer() {
+		return Buffer.concat(this.buffers, this.byteOffset);
 	}
+}
 
-	byteOffset += bodyOffset;
+function sortBlocks(blocksByTitle, blockIndices) {
+	return [...blocksByTitle].sort(
+		([aTitle], [bTitle]) => {
+			const a = blockIndices.get(aTitle);
+			const b = blockIndices.get(bTitle);
 
-	const compressed = zlib.gzipSync(Buffer.concat(buffers, byteOffset));
+			if (a === undefined) {
+				if (b === undefined) {
+					return 0;
+				}
+
+				return 1;
+			}
+
+			if (b === undefined) {
+				return -1;
+			}
+
+			return a - b;
+		},
+	);
+}
+
+async function encodeSnapshots(snapshotData) {
+	const encoded = await cbor.encodeAsync(snapshotData, {
+		omitUndefinedProperties: true,
+		canonical: true,
+	});
+	const compressed = zlib.gzipSync(encoded);
 	compressed[9] = 0x03; // Override the GZip header containing the OS to always be Linux
-	const md5sum = crypto.createHash('md5').update(compressed).digest();
+	const sha256sum = crypto.createHash('sha256').update(compressed).digest();
 	return Buffer.concat([
 		READABLE_PREFIX,
 		VERSION_HEADER,
-		md5sum,
-		compressed
-	], READABLE_PREFIX.byteLength + VERSION_HEADER.byteLength + MD5_HASH_LENGTH + compressed.byteLength);
+		sha256sum,
+		compressed,
+	], READABLE_PREFIX.byteLength + VERSION_HEADER.byteLength + SHA_256_HASH_LENGTH + compressed.byteLength);
 }
 
 function decodeSnapshots(buffer, snapPath) {
@@ -253,182 +205,207 @@ function decodeSnapshots(buffer, snapPath) {
 
 	// The version starts after the readable prefix, which is ended by a newline
 	// byte (0x0A).
-	const versionOffset = buffer.indexOf(0x0A) + 1;
+	const newline = buffer.indexOf(0x0A);
+	if (newline === -1) {
+		throw new InvalidSnapshotError(snapPath);
+	}
+
+	const versionOffset = newline + 1;
 	const version = buffer.readUInt16LE(versionOffset);
 	if (version !== VERSION) {
 		throw new VersionMismatchError(snapPath, version);
 	}
 
-	const md5sumOffset = versionOffset + 2;
-	const compressedOffset = md5sumOffset + MD5_HASH_LENGTH;
+	const sha256sumOffset = versionOffset + 2;
+	const compressedOffset = sha256sumOffset + SHA_256_HASH_LENGTH;
 	const compressed = buffer.slice(compressedOffset);
 
-	const md5sum = crypto.createHash('md5').update(compressed).digest();
-	const expectedSum = buffer.slice(md5sumOffset, compressedOffset);
-	if (!md5sum.equals(expectedSum)) {
+	const sha256sum = crypto.createHash('sha256').update(compressed).digest();
+	const expectedSum = buffer.slice(sha256sumOffset, compressedOffset);
+	if (!sha256sum.equals(expectedSum)) {
 		throw new ChecksumError(snapPath);
 	}
 
 	const decompressed = zlib.gunzipSync(compressed);
-	let byteOffset = 0;
-
-	const headerLength = decompressed.readUInt32LE(byteOffset);
-	byteOffset += 4;
-
-	const snapshotsByHash = new Map();
-	const numberHashes = decompressed.readUInt16LE(byteOffset);
-	byteOffset += 2;
-
-	for (let count = 0; count < numberHashes; count++) {
-		const hash = decompressed.toString('hex', byteOffset, byteOffset + MD5_HASH_LENGTH);
-		byteOffset += MD5_HASH_LENGTH;
-
-		const numberSnapshots = decompressed.readUInt16LE(byteOffset);
-		byteOffset += 2;
-
-		const snapshotsBuffers = new Array(numberSnapshots);
-		for (let index = 0; index < numberSnapshots; index++) {
-			const start = decompressed.readUInt32LE(byteOffset) + headerLength;
-			byteOffset += 4;
-			const end = decompressed.readUInt32LE(byteOffset) + headerLength;
-			byteOffset += 4;
-			snapshotsBuffers[index] = decompressed.slice(start, end);
-		}
-
-		// Allow for new entries to be appended to an existing header, which could
-		// lead to the same hash being present multiple times.
-		if (snapshotsByHash.has(hash)) {
-			snapshotsByHash.set(hash, snapshotsByHash.get(hash).concat(snapshotsBuffers));
-		} else {
-			snapshotsByHash.set(hash, snapshotsBuffers);
-		}
-	}
-
-	return snapshotsByHash;
+	return cbor.decode(decompressed);
 }
 
 class Manager {
 	constructor(options) {
-		this.appendOnly = options.appendOnly;
 		this.dir = options.dir;
 		this.recordNewSnapshots = options.recordNewSnapshots;
+		this.updating = options.updating;
 		this.relFile = options.relFile;
 		this.reportFile = options.reportFile;
+		this.reportPath = options.reportPath;
 		this.snapFile = options.snapFile;
 		this.snapPath = options.snapPath;
-		this.snapshotsByHash = options.snapshotsByHash;
+		this.oldBlocksByTitle = options.oldBlocksByTitle;
+		this.newBlocksByTitle = options.newBlocksByTitle;
+		this.blockIndices = new Map();
+		this.error = options.error;
 
 		this.hasChanges = false;
-		this.reportEntries = new Map();
+	}
+
+	touch(title, taskIndex) {
+		this.blockIndices.set(title, taskIndex);
 	}
 
 	compare(options) {
-		const hash = md5Hex(options.belongsTo);
-		const entries = this.snapshotsByHash.get(hash) || [];
-		const snapshotBuffer = entries[options.index];
+		if (this.error) {
+			throw this.error;
+		}
 
-		if (!snapshotBuffer) {
+		const block = this.newBlocksByTitle.get(options.belongsTo);
+
+		const snapshot = block && block.snapshots[options.index];
+		const data = snapshot && snapshot.data;
+
+		if (!data) {
 			if (!this.recordNewSnapshots) {
 				return {pass: false};
 			}
 
 			if (options.deferRecording) {
-				const record = this.deferRecord(hash, options);
+				const record = this.deferRecord(options);
 				return {pass: true, record};
 			}
 
-			this.record(hash, options);
+			this.record(options);
 			return {pass: true};
 		}
 
-		const actual = concordance.deserialize(snapshotBuffer, concordanceOptions);
+		const actual = concordance.deserialize(data, concordanceOptions);
 		const expected = concordance.describe(options.expected, concordanceOptions);
 		const pass = concordance.compareDescriptors(actual, expected);
 
 		return {actual, expected, pass};
 	}
 
-	deferRecord(hash, options) {
-		const descriptor = concordance.describe(options.expected, concordanceOptions);
-		const snapshot = concordance.serialize(descriptor);
-		const entry = formatEntry(options.label, descriptor);
-		const {taskIndex, snapIndex, associatedTaskIndex} = options;
+	recordSerialized({data, label, belongsTo, index}) {
+		let block = this.newBlocksByTitle.get(belongsTo);
+		if (!block) {
+			block = {snapshots: []};
+		}
+
+		const {snapshots} = block;
+
+		if (index > snapshots.length) {
+			throw new RangeError(`Cannot record snapshot ${index} for ${JSON.stringify(belongsTo)}, exceeds expected index of ${snapshots.length}`);
+		} else if (index < snapshots.length) {
+			if (snapshots[index].data) {
+				throw new RangeError(`Cannot record snapshot ${index} for ${JSON.stringify(belongsTo)}, already exists`);
+			}
+
+			snapshots[index] = {data, label};
+		} else {
+			snapshots.push({data, label});
+		}
+
+		this.newBlocksByTitle.set(belongsTo, block);
+	}
+
+	deferRecord(options) {
+		const {expected, belongsTo, label, index} = options;
+		const descriptor = concordance.describe(expected, concordanceOptions);
+		const data = concordance.serialize(descriptor);
 
 		return () => { // Must be called in order!
 			this.hasChanges = true;
-
-			let snapshots = this.snapshotsByHash.get(hash);
-			if (!snapshots) {
-				snapshots = [];
-				this.snapshotsByHash.set(hash, snapshots);
-			}
-
-			if (options.index > snapshots.length) {
-				throw new RangeError(`Cannot record snapshot ${options.index} for ${JSON.stringify(options.belongsTo)}, exceeds expected index of ${snapshots.length}`);
-			}
-
-			if (options.index < snapshots.length) {
-				throw new RangeError(`Cannot record snapshot ${options.index} for ${JSON.stringify(options.belongsTo)}, already exists`);
-			}
-
-			snapshots.push(snapshot);
-
-			if (this.reportEntries.has(options.belongsTo)) {
-				this.reportEntries.get(options.belongsTo).buffers.push(entry);
-			} else {
-				this.reportEntries.set(options.belongsTo, {buffers: [entry], taskIndex, snapIndex, associatedTaskIndex});
-			}
+			this.recordSerialized({data, label, belongsTo, index});
 		};
 	}
 
-	record(hash, options) {
-		const record = this.deferRecord(hash, options);
+	record(options) {
+		const record = this.deferRecord(options);
 		record();
 	}
 
-	save() {
+	skipBlock(title) {
+		const block = this.oldBlocksByTitle.get(title);
+
+		if (block) {
+			this.newBlocksByTitle.set(title, block);
+		}
+	}
+
+	skipSnapshot({belongsTo, index, deferRecording}) {
+		const oldBlock = this.oldBlocksByTitle.get(belongsTo);
+		let snapshot = oldBlock && oldBlock.snapshots[index];
+
+		if (!snapshot) {
+			snapshot = {};
+		}
+
+		// Retain the label from the old snapshot, so as not to assume that the
+		// snapshot.skip() arguments are well-formed.
+
+		// Defer recording if called in a try().
+		if (deferRecording) {
+			return () => { // Must be called in order!
+				this.recordSerialized({belongsTo, index, ...snapshot});
+			};
+		}
+
+		this.recordSerialized({belongsTo, index, ...snapshot});
+	}
+
+	async save() {
+		const {dir, relFile, snapFile, snapPath, reportPath} = this;
+
+		if (this.updating && this.newBlocksByTitle.size === 0) {
+			return {
+				changedFiles: [cleanFile(snapPath), cleanFile(reportPath)].flat(),
+				temporaryFiles: [],
+			};
+		}
+
 		if (!this.hasChanges) {
 			return null;
 		}
 
-		const {snapPath} = this;
-		const buffer = encodeSnapshots(this.snapshotsByHash);
+		const snapshots = {
+			blocks: sortBlocks(this.newBlocksByTitle, this.blockIndices).map(
+				([title, block]) => ({title, ...block}),
+			),
+		};
 
-		const reportPath = path.join(this.dir, this.reportFile);
-		const existingReport = this.appendOnly ? tryRead(reportPath) : null;
-		const reportBuffer = existingReport ?
-			appendReportEntries(existingReport, this.reportEntries) :
-			generateReport(this.relFile, this.snapFile, this.reportEntries);
+		const buffer = await encodeSnapshots(snapshots);
+		const reportBuffer = generateReport(relFile, snapFile, snapshots);
 
-		fs.mkdirSync(this.dir, {recursive: true});
+		await fs.promises.mkdir(dir, {recursive: true});
 
-		const paths = [snapPath, reportPath];
-		const tmpfileCreated = tmpfile => paths.push(tmpfile);
-		writeFileAtomic.sync(snapPath, buffer, {tmpfileCreated});
-		writeFileAtomic.sync(reportPath, reportBuffer, {tmpfileCreated});
-		return paths;
+		const temporaryFiles = [];
+		const tmpfileCreated = file => temporaryFiles.push(file);
+		await Promise.all([
+			writeFileAtomic(snapPath, buffer, {tmpfileCreated}),
+			writeFileAtomic(reportPath, reportBuffer, {tmpfileCreated}),
+		]);
+		return {
+			changedFiles: [snapPath, reportPath],
+			temporaryFiles,
+		};
 	}
 }
 
 const resolveSourceFile = mem(file => {
-	const testDir = path.dirname(file);
-	const buffer = tryRead(file);
-	if (!buffer) {
-		return file; // Assume the file is stubbed in our test suite.
+	const sourceMap = findSourceMap(file);
+	if (sourceMap === undefined) {
+		return file;
 	}
 
-	const source = buffer.toString();
-	const converter = convertSourceMap.fromSource(source) || convertSourceMap.fromMapFileSource(source, testDir);
-	if (converter) {
-		const map = converter.toObject();
-		const firstSource = `${map.sourceRoot || ''}${map.sources[0]}`;
-		return path.resolve(testDir, firstSource);
+	const {payload} = sourceMap;
+	if (payload.sources.length === 0) { // Hypothetical?
+		return file;
 	}
 
-	return file;
+	return payload.sources[0].startsWith('file://')
+		? fileURLToPath(payload.sources[0])
+		: payload.sources[0];
 });
 
-const determineSnapshotDir = mem(({file, fixedLocation, projectDir}) => {
+export const determineSnapshotDir = mem(({file, fixedLocation, projectDir}) => {
 	const testDir = path.dirname(resolveSourceFile(file));
 	if (fixedLocation) {
 		const relativeTestLocation = path.relative(projectDir, testDir);
@@ -447,8 +424,6 @@ const determineSnapshotDir = mem(({file, fixedLocation, projectDir}) => {
 	return testDir;
 }, {cacheKey: ([{file}]) => file});
 
-exports.determineSnapshotDir = determineSnapshotDir;
-
 function determineSnapshotPaths({file, fixedLocation, projectDir}) {
 	const dir = determineSnapshotDir({file, fixedLocation, projectDir});
 	const relFile = path.relative(projectDir, resolveSourceFile(file));
@@ -460,7 +435,9 @@ function determineSnapshotPaths({file, fixedLocation, projectDir}) {
 		dir,
 		relFile,
 		snapFile,
-		reportFile
+		reportFile,
+		snapPath: path.join(dir, snapFile),
+		reportPath: path.join(dir, reportFile),
 	};
 }
 
@@ -477,45 +454,52 @@ function cleanFile(file) {
 	}
 }
 
-// Remove snapshot and report if they exist. Returns an array containing the
-// paths of the touched files.
-function cleanSnapshots({file, fixedLocation, projectDir}) {
-	const {dir, snapFile, reportFile} = determineSnapshotPaths({file, fixedLocation, projectDir});
+export function load({file, fixedLocation, projectDir, recordNewSnapshots, updating}) {
+	// Keep runner unit tests that use `new Runner()` happy
+	if (file === undefined || projectDir === undefined) {
+		return new Manager({
+			recordNewSnapshots,
+			updating,
+			oldBlocksByTitle: new Map(),
+			newBlocksByTitle: new Map(),
+		});
+	}
 
-	return [
-		...cleanFile(path.join(dir, snapFile)),
-		...cleanFile(path.join(dir, reportFile))
-	];
-}
+	const paths = determineSnapshotPaths({file, fixedLocation, projectDir});
+	const buffer = tryRead(paths.snapPath);
 
-exports.cleanSnapshots = cleanSnapshots;
+	if (!buffer) {
+		return new Manager({
+			recordNewSnapshots,
+			updating,
+			...paths,
+			oldBlocksByTitle: new Map(),
+			newBlocksByTitle: new Map(),
+		});
+	}
 
-function load({file, fixedLocation, projectDir, recordNewSnapshots, updating}) {
-	const {dir, relFile, snapFile, reportFile} = determineSnapshotPaths({file, fixedLocation, projectDir});
-	const snapPath = path.join(dir, snapFile);
+	let blocksByTitle;
+	let snapshotError;
 
-	let appendOnly = !updating;
-	let snapshotsByHash;
+	try {
+		const data = decodeSnapshots(buffer, paths.snapPath);
+		blocksByTitle = new Map(data.blocks.map(({title, ...block}) => [title, block]));
+	} catch (error) {
+		blocksByTitle = new Map();
 
-	if (!updating) {
-		const buffer = tryRead(snapPath);
-		if (buffer) {
-			snapshotsByHash = decodeSnapshots(buffer, snapPath);
-		} else {
-			appendOnly = false;
+		if (!updating) { // Discard all decoding errors when updating snapshots
+			snapshotError = error instanceof SnapshotError
+				? error
+				: new InvalidSnapshotError(paths.snapPath);
 		}
 	}
 
 	return new Manager({
-		appendOnly,
-		dir,
 		recordNewSnapshots,
-		relFile,
-		reportFile,
-		snapFile,
-		snapPath,
-		snapshotsByHash: snapshotsByHash || new Map()
+		updating,
+		...paths,
+		oldBlocksByTitle: blocksByTitle,
+		newBlocksByTitle: updating ? new Map() : blocksByTitle,
+		error: snapshotError,
 	});
 }
-
-exports.load = load;