diff --git a/lib/concurrent.js b/lib/concurrent.js
index 679a5196e..43e842ea7 100644
--- a/lib/concurrent.js
+++ b/lib/concurrent.js
@@ -6,7 +6,7 @@ var BAIL_ERROR = new Error();
 module.exports = Concurrent;
 
 function Concurrent(tests, bail) {
-	if (!this instanceof Concurrent) {
+	if (!(this instanceof Concurrent)) {
 		throw new TypeError('Class constructor Concurrent cannot be invoked without \'new\'');
 	}
 
diff --git a/lib/sequence.js b/lib/sequence.js
index 01ff36afe..f88aabf39 100644
--- a/lib/sequence.js
+++ b/lib/sequence.js
@@ -4,7 +4,7 @@ var isPromise = require('is-promise');
 module.exports = Sequence;
 
 function Sequence(tests, bail) {
-	if (!this instanceof Sequence) {
+	if (!(this instanceof Sequence)) {
 		throw new TypeError('Class constructor Sequence cannot be invoked without \'new\'');
 	}
 
diff --git a/test/api.js b/test/api.js
index faa32e07e..146bcbfab 100644
--- a/test/api.js
+++ b/test/api.js
@@ -6,6 +6,14 @@ var fs = require('fs');
 var test = require('tap').test;
 var Api = require('../api');
 
+test('must be called with new', function (t) {
+	t.throws(function () {
+		var api = Api;
+		api([path.join(__dirname, 'fixture/es2015.js')]);
+	}, {message: 'Class constructor Api cannot be invoked without \'new\''});
+	t.end();
+});
+
 test('ES2015 support', function (t) {
 	t.plan(1);
 
diff --git a/test/ava-error.js b/test/ava-error.js
new file mode 100644
index 000000000..dda19eda2
--- /dev/null
+++ b/test/ava-error.js
@@ -0,0 +1,11 @@
+'use strict';
+var test = require('tap').test;
+var AvaError = require('../lib/ava-error');
+
+test('must be called with new', function (t) {
+	t.throws(function () {
+		var avaError = AvaError;
+		avaError('test message');
+	}, {message: 'Class constructor AvaError cannot be invoked without \'new\''});
+	t.end();
+});
diff --git a/test/caching-precompiler.js b/test/caching-precompiler.js
index 2e1a0edcb..27b972911 100644
--- a/test/caching-precompiler.js
+++ b/test/caching-precompiler.js
@@ -5,7 +5,6 @@ var test = require('tap').test;
 var uniqueTempDir = require('unique-temp-dir');
 
 var CachingPrecompiler = require('../lib/caching-precompiler');
-var createCachingPrecompiler = CachingPrecompiler;
 
 function fixture(name) {
 	return path.join(__dirname, 'fixture', name);
@@ -26,10 +25,11 @@ test('creation with new', function (t) {
 	t.end();
 });
 
-test('creation without new throws', function (t) {
+test('must be called with new', function (t) {
 	t.throws(function () {
-		createCachingPrecompiler(uniqueTempDir());
-	});
+		var cachingPrecompiler = CachingPrecompiler;
+		cachingPrecompiler(uniqueTempDir());
+	}, {message: 'Class constructor CachingPrecompiler cannot be invoked without \'new\''});
 	t.end();
 });
 
diff --git a/test/concurrent.js b/test/concurrent.js
index 377201dbd..8e48bcd95 100644
--- a/test/concurrent.js
+++ b/test/concurrent.js
@@ -610,9 +610,9 @@ test('rejections are just passed through - bail', function (t) {
 
 test('must be called with new', function (t) {
 	t.throws(function () {
-		var c = Concurrent;
-		c([pass('a')]);
-	});
+		var concurrent = Concurrent;
+		concurrent([pass('a')]);
+	}, {message: 'Class constructor Concurrent cannot be invoked without \'new\''});
 	t.end();
 });
 
diff --git a/test/logger.js b/test/logger.js
new file mode 100644
index 000000000..d1132efe7
--- /dev/null
+++ b/test/logger.js
@@ -0,0 +1,11 @@
+'use strict';
+var test = require('tap').test;
+var Logger = require('../lib/logger');
+
+test('must be called with new', function (t) {
+	t.throws(function () {
+		var logger = Logger;
+		logger();
+	}, {message: 'Class constructor Logger cannot be invoked without \'new\''});
+	t.end();
+});
diff --git a/test/runner.js b/test/runner.js
index e405bd4f7..a95c30d7e 100644
--- a/test/runner.js
+++ b/test/runner.js
@@ -4,6 +4,14 @@ var Runner = require('../lib/runner');
 
 var noop = function () {};
 
+test('must be called with new', function (t) {
+	t.throws(function () {
+		var runner = Runner;
+		runner();
+	}, {message: 'Class constructor Runner cannot be invoked without \'new\''});
+	t.end();
+});
+
 test('runner emits a "test" event', function (t) {
 	var runner = new Runner();
 
diff --git a/test/sequence.js b/test/sequence.js
index 21dde90b0..41c3d8b7a 100644
--- a/test/sequence.js
+++ b/test/sequence.js
@@ -609,7 +609,14 @@ test('must be called with new', function (t) {
 	t.throws(function () {
 		var sequence = Sequence;
 		sequence([pass('a')]);
-	});
+	}, {message: 'Class constructor Sequence cannot be invoked without \'new\''});
+	t.end();
+});
+
+test('needs at least one sequence item', function (t) {
+	t.throws(function () {
+		new Sequence().run();
+	}, {message: 'Sequence items can\'t be undefined'});
 	t.end();
 });
 
diff --git a/test/test-collection.js b/test/test-collection.js
index f42eff1c3..c7d37e581 100644
--- a/test/test-collection.js
+++ b/test/test-collection.js
@@ -45,11 +45,11 @@ function serialize(collection) {
 	return ret;
 }
 
-test('requires new', function (t) {
-	var withoutNew = TestCollection;
+test('must be called with new', function (t) {
+	var testCollection = TestCollection;
 	t.throws(function () {
-		withoutNew();
-	});
+		testCollection();
+	}, {message: 'Class constructor TestCollection cannot be invoked without \'new\''});
 	t.end();
 });
 
diff --git a/test/test.js b/test/test.js
index 194433b59..8d8a73c03 100644
--- a/test/test.js
+++ b/test/test.js
@@ -17,6 +17,14 @@ ava.cb = function (title, fn, contextRef, report) {
 	return t;
 };
 
+test('must be called with new', function (t) {
+	t.throws(function () {
+		var test = Test;
+		test();
+	}, {message: 'Class constructor Test cannot be invoked without \'new\''});
+	t.end();
+});
+
 test('run test', function (t) {
 	var result = ava('foo', function (a) {
 		a.fail();