Draft and lifecycles directories cleanup (#2122)

* Move Pausable into utils

* Move Strings into utils

* Move Counters into utils

* Move SignedSafeMath into math

* Remove ERC1046

* Make ERC20Snapshot.snapshot internal

* Move ERC20Snapshot into ERC20

* Add drafts deprecation notice

* Remove drafts directory

* Add changelog entry

* Apply suggestions from code review

Co-Authored-By: Francisco Giordano <frangio.1@gmail.com>

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

test/utils/Counters.test.js

@@ -0,0 +1,61 @@
+const { contract } = require('@openzeppelin/test-environment');
+const { expectRevert } = require('@openzeppelin/test-helpers');
+
+const { expect } = require('chai');
+
+const CountersImpl = contract.fromArtifact('CountersImpl');
+
+describe('Counters', function () {
+  beforeEach(async function () {
+    this.counter = await CountersImpl.new();
+  });
+
+  it('starts at zero', async function () {
+    expect(await this.counter.current()).to.be.bignumber.equal('0');
+  });
+
+  describe('increment', function () {
+    it('increments the current value by one', async function () {
+      await this.counter.increment();
+      expect(await this.counter.current()).to.be.bignumber.equal('1');
+    });
+
+    it('can be called multiple times', async function () {
+      await this.counter.increment();
+      await this.counter.increment();
+      await this.counter.increment();
+
+      expect(await this.counter.current()).to.be.bignumber.equal('3');
+    });
+  });
+
+  describe('decrement', function () {
+    beforeEach(async function () {
+      await this.counter.increment();
+      expect(await this.counter.current()).to.be.bignumber.equal('1');
+    });
+
+    it('decrements the current value by one', async function () {
+      await this.counter.decrement();
+      expect(await this.counter.current()).to.be.bignumber.equal('0');
+    });
+
+    it('reverts if the current value is 0', async function () {
+      await this.counter.decrement();
+      await expectRevert(this.counter.decrement(), 'SafeMath: subtraction overflow');
+    });
+
+    it('can be called multiple times', async function () {
+      await this.counter.increment();
+      await this.counter.increment();
+
+      expect(await this.counter.current()).to.be.bignumber.equal('3');
+
+      await this.counter.decrement();
+      await this.counter.decrement();
+      await this.counter.decrement();
+
+      expect(await this.counter.current()).to.be.bignumber.equal('0');
+    });
+  });
+});