test: improve assert messages in test-global

PR-URL: #16843
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: markmcnelis

test/parallel/test-global.js

@@ -34,17 +34,18 @@ baseFoo = 'foo'; // eslint-disable-line no-undef
 global.baseBar='bar';
 
 assert.strictEqual(global.baseFoo,'foo',
-'x -> global.x in base level not working');
+`x -> global.x failed: global.baseFoo = ${global.baseFoo}`);
 
 assert.strictEqual(baseBar,// eslint-disable-line no-undef
 'bar',
-'global.x -> x in base level not working');
+// eslint-disable-next-line no-undef
+`global.x -> x failed: baseBar = ${baseBar}`);
 
 constmod=require(fixtures.path('global','plain'));
 constfooBar=mod.fooBar;
 
-assert.strictEqual(fooBar.foo,'foo','x -> global.x in sub level not working');
+assert.strictEqual(fooBar.foo,'foo');
 
-assert.strictEqual(fooBar.bar,'bar','global.x -> x in sub level not working');
+assert.strictEqual(fooBar.bar,'bar');
 
 assert.strictEqual(Object.prototype.toString.call(global),'[object global]');