Add ERC20 opt-in migration contract (#1054)

* Extract standard token behaviuor to reuse it in other tests

* Add opt in ERC20 migration contract

* Make migration contract not to depend from standard token

* Changes based on feedback

* Improve MigratableERC20 inline documentation

* move behaviors to behaviors directory

* refactor MigratableERC20 into ERC20Migrator

* fix errors

* change expectEvent to support multiple events with same name

* fix tests

* update documentation

* rename MigratableERC20 files to ERC20Migrator

* move to drafts

* test beginMigration

* rename to ERC20Migrator

* missing semicolon  (╯°□°）╯︵ ┻━┻

* add non-zero check

* improve documentation based on review comments

* improve test descriptions

* improve docs

* add getters

* fix contract

* improve tests

test/helpers/expectEvent.js

@@ -1,12 +1,24 @@
 const should = require('chai').should();
 
 function inLogs (logs, eventName, eventArgs = {}) {
-  const event = logs.find(e => e.event === eventName);
+  const event = logs.find(function (e) {
+    if (e.event === eventName) {
+      let matches = true;
+
+      for (const [k, v] of Object.entries(eventArgs)) {
+        if (e.args[k] !== v) {
+          matches = false;
+        }
+      }
+
+      if (matches) {
+        return true;
+      }
+    }
+  });
+
   should.exist(event);
-  for (const [k, v] of Object.entries(eventArgs)) {
-    should.exist(event.args[k]);
-    event.args[k].should.equal(v);
-  }
+
   return event;
 }