Add a VestingWallet (#2748)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

test/finance/VestingWallet.behavior.js

@@ -0,0 +1,72 @@
+const { expectEvent } = require('@openzeppelin/test-helpers');
+const { expect } = require('chai');
+
+function releasedEvent (token, amount) {
+  return token
+    ? [ 'ERC20Released', { token: token.address, amount } ]
+    : [ 'EtherReleased', { amount } ];
+}
+
+function shouldBehaveLikeVesting (beneficiary) {
+  it('check vesting schedule', async function () {
+    const [ method, ...args ] = this.token
+      ? [ 'vestedAmount(address,uint64)', this.token.address ]
+      : [ 'vestedAmount(uint64)' ];
+
+    for (const timestamp of this.schedule) {
+      expect(await this.mock.methods[method](...args, timestamp))
+        .to.be.bignumber.equal(this.vestingFn(timestamp));
+    }
+  });
+
+  it('execute vesting schedule', async function () {
+    const [ method, ...args ] = this.token
+      ? [ 'release(address)', this.token.address ]
+      : [ 'release()' ];
+
+    let released = web3.utils.toBN(0);
+    const before = await this.getBalance(beneficiary);
+
+    {
+      const receipt = await this.mock.methods[method](...args);
+
+      await expectEvent.inTransaction(
+        receipt.tx,
+        this.mock,
+        ...releasedEvent(this.token, '0'),
+      );
+
+      await this.checkRelease(receipt, beneficiary, '0');
+
+      expect(await this.getBalance(beneficiary)).to.be.bignumber.equal(before);
+    }
+
+    for (const timestamp of this.schedule) {
+      const vested = this.vestingFn(timestamp);
+
+      await new Promise(resolve => web3.currentProvider.send({
+        method: 'evm_setNextBlockTimestamp',
+        params: [ timestamp.toNumber() ],
+      }, resolve));
+
+      const receipt = await this.mock.methods[method](...args);
+
+      await expectEvent.inTransaction(
+        receipt.tx,
+        this.mock,
+        ...releasedEvent(this.token, vested.sub(released)),
+      );
+
+      await this.checkRelease(receipt, beneficiary, vested.sub(released));
+
+      expect(await this.getBalance(beneficiary))
+        .to.be.bignumber.equal(before.add(vested));
+
+      released = vested;
+    }
+  });
+}
+
+module.exports = {
+  shouldBehaveLikeVesting,
+};