Add test cases for formatting nil type as Void

analyzer/type_test.go

@@ -162,3 +162,19 @@ testString (test,
 Bird: (~ [fly] [land])
 `)
 }
+
+func TestTypeIntegerLiteralVoid (test *testing.T) {
+testStringErr (test,
+"cannot use integer literal as Void", 2, 10,
+`
+[main] = 5
+`)
+}
+
+func TestTypeStringLiteralVoid (test *testing.T) {
+testStringErr (test,
+"cannot use string literal as Void", 2, 10,
+`
+[main] = 'hello'
+`)
+}