test: increase coverage for assertion_error.js

Add a test for long strings and assert.notDeepEqual() to cover code that
truncates output when it is longer than 1024 characters.

Author: Trott

test/parallel/test-assert-deep.js

@@ -653,16 +653,22 @@ assertDeepAndStrictEqual(-0, -0);
 
 assert.deepEqual(new Date(2000, 3, 14), new Date(2000, 3, 14));
 
-assert.throws(() => assert.deepEqual(new Date(), new Date(2000, 3, 14)),
+assert.throws(() => { assert.deepEqual(new Date(), new Date(2000, 3, 14)); },
               AssertionError,
               'deepEqual(new Date(), new Date(2000, 3, 14))');
 
 assert.throws(
-  () => assert.notDeepEqual(new Date(2000, 3, 14), new Date(2000, 3, 14)),
+  () => { assert.notDeepEqual(new Date(2000, 3, 14), new Date(2000, 3, 14)); },
   AssertionError,
   'notDeepEqual(new Date(2000, 3, 14), new Date(2000, 3, 14))'
 );
 
+assert.throws(
+  () => { assert.notDeepEqual('a'.repeat(1024), 'a'.repeat(1024)); },
+  AssertionError,
+  'notDeepEqual("a".repeat(1024), "a".repeat(1024))'
+);
+
 assert.notDeepEqual(new Date(), new Date(2000, 3, 14));
 
 assertDeepAndStrictEqual(/a/, /a/);