add tests for direct instantiation

Author: jonchurch

test/test.js

@@ -184,13 +184,20 @@ describe('Subclass Instantiation', function () {
       // eslint-disable-next-line no-new
       new createError.NotFound()
     })
+    assert.doesNotThrow(() => {
+      // eslint-disable-next-line no-new
+      createError.NotFound()
+    })
   })
 
   it('should allow instantiation of ServerError subclasses', function () {
     assert.doesNotThrow(() => {
       // eslint-disable-next-line no-new
       new createError.InternalServerError()
     })
+    assert.doesNotThrow(() => {
+      createError.InternalServerError()
+    })
   })
 })
 
@@ -369,6 +376,10 @@ describe('HTTP Errors', function () {
     assert.throws(function () {
       new createError.HttpError() // eslint-disable-line no-new
     }, /cannot construct abstract class/)
+
+    assert.throws(function () {
+      createError.HttpError()
+    }, /cannot construct abstract class/)
   })
 
   it('new createError.NotFound()', function () {