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/Pausable.test.js

@@ -0,0 +1,91 @@
+const { accounts, contract } = require('@openzeppelin/test-environment');
+
+const { expectEvent, expectRevert } = require('@openzeppelin/test-helpers');
+
+const { expect } = require('chai');
+
+const PausableMock = contract.fromArtifact('PausableMock');
+
+describe('Pausable', function () {
+  const [ pauser ] = accounts;
+
+  beforeEach(async function () {
+    this.pausable = await PausableMock.new();
+  });
+
+  context('when unpaused', function () {
+    beforeEach(async function () {
+      expect(await this.pausable.paused()).to.equal(false);
+    });
+
+    it('can perform normal process in non-pause', async function () {
+      expect(await this.pausable.count()).to.be.bignumber.equal('0');
+
+      await this.pausable.normalProcess();
+      expect(await this.pausable.count()).to.be.bignumber.equal('1');
+    });
+
+    it('cannot take drastic measure in non-pause', async function () {
+      await expectRevert(this.pausable.drasticMeasure(),
+        'Pausable: not paused'
+      );
+      expect(await this.pausable.drasticMeasureTaken()).to.equal(false);
+    });
+
+    context('when paused', function () {
+      beforeEach(async function () {
+        ({ logs: this.logs } = await this.pausable.pause({ from: pauser }));
+      });
+
+      it('emits a Paused event', function () {
+        expectEvent.inLogs(this.logs, 'Paused', { account: pauser });
+      });
+
+      it('cannot perform normal process in pause', async function () {
+        await expectRevert(this.pausable.normalProcess(), 'Pausable: paused');
+      });
+
+      it('can take a drastic measure in a pause', async function () {
+        await this.pausable.drasticMeasure();
+        expect(await this.pausable.drasticMeasureTaken()).to.equal(true);
+      });
+
+      it('reverts when re-pausing', async function () {
+        await expectRevert(this.pausable.pause(), 'Pausable: paused');
+      });
+
+      describe('unpausing', function () {
+        it('is unpausable by the pauser', async function () {
+          await this.pausable.unpause();
+          expect(await this.pausable.paused()).to.equal(false);
+        });
+
+        context('when unpaused', function () {
+          beforeEach(async function () {
+            ({ logs: this.logs } = await this.pausable.unpause({ from: pauser }));
+          });
+
+          it('emits an Unpaused event', function () {
+            expectEvent.inLogs(this.logs, 'Unpaused', { account: pauser });
+          });
+
+          it('should resume allowing normal process', async function () {
+            expect(await this.pausable.count()).to.be.bignumber.equal('0');
+            await this.pausable.normalProcess();
+            expect(await this.pausable.count()).to.be.bignumber.equal('1');
+          });
+
+          it('should prevent drastic measure', async function () {
+            await expectRevert(this.pausable.drasticMeasure(),
+              'Pausable: not paused'
+            );
+          });
+
+          it('reverts when re-unpausing', async function () {
+            await expectRevert(this.pausable.unpause(), 'Pausable: not paused');
+          });
+        });
+      });
+    });
+  });
+});