Ensure different OSes generate consistent snapshots

Fixes #1786.

lib/snapshot-manager.js

@@ -11,6 +11,7 @@ const indentString = require('indent-string');
 const makeDir = require('make-dir');
 const md5Hex = require('md5-hex');
 const convertSourceMap = require('convert-source-map');
+const slash = require('slash');
 
 const concordanceOptions = require('./concordance-options').snapshotManager;
 
@@ -128,7 +129,7 @@ function generateReport(relFile, snapFile, entries) {
 	const buffers = combined.buffers;
 	let byteLength = combined.byteLength;
 
-	const header = Buffer.from(`# Snapshot report for \`${relFile}\`
+	const header = Buffer.from(`# Snapshot report for \`${slash(relFile)}\`
 
 The actual snapshot is saved in \`${snapFile}\`.
 
@@ -210,6 +211,7 @@ function encodeSnapshots(buffersByHash) {
 	byteOffset += bodyOffset;
 
 	const compressed = zlib.gzipSync(Buffer.concat(buffers, byteOffset));
+	compressed[9] = 0x03; // Override the GZip header containing the OS to always be Linux
 	const md5sum = crypto.createHash('md5').update(compressed).digest();
 	return Buffer.concat([
 		READABLE_PREFIX,

test/fixture/snapshots/test-content/package.json

@@ -0,0 +1,5 @@
+{
+	"ava": {
+		"files": "tests"
+	}
+}

test/fixture/snapshots/test-content/test.js.md.expected

@@ -0,0 +1,13 @@
+# Snapshot report for `tests/test.js`
+
+The actual snapshot is saved in `test.js.snap`.
+
+Generated by [AVA](https://ava.li).
+
+## test title
+
+> Snapshot 1
+
+    {
+      foo: 'bar',
+    }

test/fixture/snapshots/test-content/tests/test.js

@@ -0,0 +1,5 @@
+import test from '../../../../..';
+
+test('test title', t => {
+	t.snapshot({foo: 'bar'});
+});

test/integration/snapshots.js

@@ -205,3 +205,40 @@ test('snapshots resolved location from "snapshotDir" in AVA config', t => {
 		t.end();
 	});
 });
+
+test(`snapshots are indentical on different platforms`, t => {
+	const fixtureDir = path.join(__dirname, '..', 'fixture', 'snapshots', 'test-content');
+	const reportPath = path.join(fixtureDir, 'tests', 'snapshots', 'test.js.md');
+	const snapPath = path.join(fixtureDir, 'tests', 'snapshots', 'test.js.snap');
+	const expectedReportPath = path.join(fixtureDir, 'test.js.md.expected');
+	const expectedSnapPath = path.join(fixtureDir, 'test.js.snap.expected');
+
+	const removeFile = filePath => {
+		try {
+			fs.unlinkSync(filePath);
+		} catch (err) {
+			if (err.code !== 'ENOENT') {
+				throw err;
+			}
+		}
+	};
+
+	// Clear current snapshots
+	[reportPath, snapPath].forEach(fp => removeFile(fp));
+
+	// Test should pass, and a snapshot gets written
+	execCli(['--update-snapshots'], {dirname: fixtureDir}, err => {
+		t.ifError(err);
+		t.true(fs.existsSync(reportPath));
+		t.true(fs.existsSync(snapPath));
+
+		const reportContents = fs.readFileSync(reportPath);
+		const snapContents = fs.readFileSync(snapPath);
+		const expectedReportContents = fs.readFileSync(expectedReportPath);
+		const expectedSnapContents = fs.readFileSync(expectedSnapPath);
+
+		t.true(reportContents.equals(expectedReportContents), 'report file contents matches snapshot');
+		t.true(snapContents.equals(expectedSnapContents), 'snap file contents matches snapshot');
+		t.end();
+	});
+});