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/token/ERC20/behaviors/ERC20Mintable.behavior.js

@@ -0,0 +1,152 @@
+const { assertRevert } = require('../../../helpers/assertRevert');
+const expectEvent = require('../../../helpers/expectEvent');
+
+const BigNumber = web3.BigNumber;
+
+require('chai')
+  .use(require('chai-bignumber')(BigNumber))
+  .should();
+
+function shouldBehaveLikeERC20Mintable (minter, [anyone]) {
+  const ZERO_ADDRESS = '0x0000000000000000000000000000000000000000';
+
+  describe('as a mintable token', function () {
+    describe('mintingFinished', function () {
+      context('when token minting is not finished', function () {
+        it('returns false', async function () {
+          (await this.token.mintingFinished()).should.equal(false);
+        });
+      });
+
+      context('when token minting is finished', function () {
+        beforeEach(async function () {
+          await this.token.finishMinting({ from: minter });
+        });
+
+        it('returns true', async function () {
+          (await this.token.mintingFinished()).should.equal(true);
+        });
+      });
+    });
+
+    describe('finishMinting', function () {
+      context('when the sender has minting permission', function () {
+        const from = minter;
+
+        context('when token minting was not finished', function () {
+          it('finishes token minting', async function () {
+            await this.token.finishMinting({ from });
+
+            (await this.token.mintingFinished()).should.equal(true);
+          });
+
+          it('emits a mint finished event', async function () {
+            const { logs } = await this.token.finishMinting({ from });
+
+            await expectEvent.inLogs(logs, 'MintingFinished');
+          });
+        });
+
+        context('when token minting was already finished', function () {
+          beforeEach(async function () {
+            await this.token.finishMinting({ from });
+          });
+
+          it('reverts', async function () {
+            await assertRevert(this.token.finishMinting({ from }));
+          });
+        });
+      });
+
+      context('when the sender doesn\'t have minting permission', function () {
+        const from = anyone;
+
+        context('when token minting was not finished', function () {
+          it('reverts', async function () {
+            await assertRevert(this.token.finishMinting({ from }));
+          });
+        });
+
+        context('when token minting was already finished', function () {
+          beforeEach(async function () {
+            await this.token.finishMinting({ from: minter });
+          });
+
+          it('reverts', async function () {
+            await assertRevert(this.token.finishMinting({ from }));
+          });
+        });
+      });
+    });
+
+    describe('mint', function () {
+      const amount = 100;
+
+      context('when the sender has minting permission', function () {
+        const from = minter;
+
+        context('when token minting is not finished', function () {
+          context('for a zero amount', function () {
+            shouldMint(0);
+          });
+
+          context('for a non-zero amount', function () {
+            shouldMint(amount);
+          });
+
+          function shouldMint (amount) {
+            beforeEach(async function () {
+              ({ logs: this.logs } = await this.token.mint(anyone, amount, { from }));
+            });
+
+            it('mints the requested amount', async function () {
+              (await this.token.balanceOf(anyone)).should.be.bignumber.equal(amount);
+            });
+
+            it('emits a mint and a transfer event', async function () {
+              const transferEvent = expectEvent.inLogs(this.logs, 'Transfer', {
+                from: ZERO_ADDRESS,
+                to: anyone,
+              });
+              transferEvent.args.value.should.be.bignumber.equal(amount);
+            });
+          }
+        });
+
+        context('when token minting is finished', function () {
+          beforeEach(async function () {
+            await this.token.finishMinting({ from: minter });
+          });
+
+          it('reverts', async function () {
+            await assertRevert(this.token.mint(anyone, amount, { from }));
+          });
+        });
+      });
+
+      context('when the sender doesn\'t have minting permission', function () {
+        const from = anyone;
+
+        context('when token minting is not finished', function () {
+          it('reverts', async function () {
+            await assertRevert(this.token.mint(anyone, amount, { from }));
+          });
+        });
+
+        context('when token minting is already finished', function () {
+          beforeEach(async function () {
+            await this.token.finishMinting({ from: minter });
+          });
+
+          it('reverts', async function () {
+            await assertRevert(this.token.mint(anyone, amount, { from }));
+          });
+        });
+      });
+    });
+  });
+}
+
+module.exports = {
+  shouldBehaveLikeERC20Mintable,
+};