Detect t.try() usage in hooks; experimentally disable t.snapshot()

`t.try()` has never worked in hooks. Fail the hook properly instead of letting it crash.

`t.snapshot()` sort of works, but not really. Add an experiment so support can be disabled. This will become the default behavior in the next major AVA release.

Fixes #2523.

Co-authored-by: Mark Wubben <mark@novemberborn.net>

lib/assert.js

@@ -258,7 +258,8 @@ class Assertions {
 		skip = notImplemented,
 		compareWithSnapshot = notImplemented,
 		powerAssert,
-		experiments = {}
+		experiments = {},
+		disableSnapshots = false
 	} = {}) {
 		const withSkip = assertionFn => {
 			assertionFn.skip = skip;
@@ -699,6 +700,15 @@ class Assertions {
 		});
 
 		this.snapshot = withSkip((expected, ...rest) => {
+			if (disableSnapshots && experiments.disableSnapshotsInHooks) {
+				fail(new AssertionError({
+					assertion: 'snapshot',
+					message: '`t.snapshot()` can only be used in tests',
+					improperUsage: true
+				}));
+				return;
+			}
+
 			let message;
 			let snapshotOptions;
 			if (rest.length > 1) {

lib/load-config.js

@@ -7,7 +7,7 @@ const pkgConf = require('pkg-conf');
 
 const NO_SUCH_FILE = Symbol('no ava.config.js file');
 const MISSING_DEFAULT_EXPORT = Symbol('missing default export');
-const EXPERIMENTS = new Set(['likeAssertion', 'reverseTeardowns']);
+const EXPERIMENTS = new Set(['disableSnapshotsInHooks', 'likeAssertion', 'reverseTeardowns']);
 
 // *Very* rudimentary support for loading ava.config.js files containing an `export default` statement.
 const evaluateJsConfig = configFile => {

lib/test.js

@@ -40,7 +40,8 @@ class ExecutionContext extends assert.Assertions {
 				return test.compareWithSnapshot(options);
 			},
 			powerAssert: test.powerAssert,
-			experiments: test.experiments
+			experiments: test.experiments,
+			disableSnapshots: test.isHook === true
 		});
 		testMap.set(this, test);
 
@@ -74,6 +75,12 @@ class ExecutionContext extends assert.Assertions {
 		};
 
 		this.try = async (...attemptArgs) => {
+			if (test.isHook) {
+				const error = new Error('`t.try()` can only be used in tests');
+				test.saveFirstError(error);
+				throw error;
+			}
+
 			const {args, buildTitle, implementations, receivedImplementationArray} = parseTestArgs(attemptArgs);
 
 			if (implementations.length === 0) {

test/helpers/exec.js

@@ -44,6 +44,7 @@ exports.fixture = async (...args) => {
 	const errors = new WeakMap();
 	const stats = {
 		failed: [],
+		failedHooks: [],
 		passed: [],
 		skipped: [],
 		uncaughtExceptions: [],
@@ -59,6 +60,14 @@ exports.fixture = async (...args) => {
 		}
 
 		switch (statusEvent.type) {
+			case 'hook-failed': {
+				const {title, testFile} = statusEvent;
+				const statObject = {title, file: normalizePath(cwd, testFile)};
+				errors.set(statObject, statusEvent.err);
+				stats.failedHooks.push(statObject);
+				break;
+			}
+
 			case 'selected-test': {
 				if (statusEvent.skip) {
 					const {title, testFile} = statusEvent;
@@ -108,6 +117,7 @@ exports.fixture = async (...args) => {
 		throw Object.assign(error, {stats});
 	} finally {
 		stats.failed.sort(compareStatObjects);
+		stats.failedHooks.sort(compareStatObjects);
 		stats.passed.sort(compareStatObjects);
 		stats.skipped.sort(compareStatObjects);
 		stats.unsavedSnapshots.sort(compareStatObjects);

test/hook-restrictions/fixtures/invalid-snapshots-in-hooks.js

@@ -0,0 +1,9 @@
+const test = require('ava');
+
+test.before(t => {
+	t.snapshot({});
+});
+
+test('cannot use snapshot in hook', t => {
+	t.pass();
+});

test/hook-restrictions/fixtures/invalid-t-try-in-hooks.js

@@ -0,0 +1,9 @@
+const test = require('ava');
+
+test.before(async t => {
+	await t.try(tt => tt.pass());
+});
+
+test('cannot use `t.try()` in hook', t => {
+	t.pass();
+});

test/hook-restrictions/fixtures/package.json

@@ -0,0 +1,10 @@
+{
+  "ava": {
+    "files": [
+      "*.js"
+    ],
+    "nonSemVerExperiments": {
+      "disableSnapshotsInHooks": true
+    }
+  }
+}

test/hook-restrictions/snapshots/test.js.md

@@ -0,0 +1,17 @@
+# Snapshot report for `test/hook-restrictions/test.js`
+
+The actual snapshot is saved in `test.js.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## `t.try()` cannot be used in hooks
+
+> error message
+
+    '`t.try()` can only be used in tests'
+
+## snapshots cannot be used in hooks
+
+> error message
+
+    '`t.snapshot()` can only be used in tests'

test/hook-restrictions/test.js

@@ -0,0 +1,14 @@
+const test = require('@ava/test');
+const exec = require('../helpers/exec');
+
+test('snapshots cannot be used in hooks', async t => {
+	const result = await t.throwsAsync(exec.fixture('invalid-snapshots-in-hooks.js'));
+	const error = result.stats.getError(result.stats.failedHooks[0]);
+	t.snapshot(error.message, 'error message');
+});
+
+test('`t.try()` cannot be used in hooks', async t => {
+	const result = await t.throwsAsync(exec.fixture('invalid-t-try-in-hooks.js'));
+	const error = result.stats.getError(result.stats.failedHooks[0]);
+	t.snapshot(error.message, 'error message');
+});