Update docs

test/utils/math/SignedMath.test.js

@@ -0,0 +1,95 @@
+const { BN, constants } = require('@openzeppelin/test-helpers');
+const { expect } = require('chai');
+const { MIN_INT256, MAX_INT256 } = constants;
+
+const SignedMath = artifacts.require('$SignedMath');
+
+contract('SignedMath', function () {
+  const min = new BN('-1234');
+  const max = new BN('5678');
+
+  beforeEach(async function () {
+    this.math = await SignedMath.new();
+  });
+
+  describe('max', function () {
+    it('is correctly detected in first argument position', async function () {
+      expect(await this.math.$max(max, min)).to.be.bignumber.equal(max);
+    });
+
+    it('is correctly detected in second argument position', async function () {
+      expect(await this.math.$max(min, max)).to.be.bignumber.equal(max);
+    });
+  });
+
+  describe('min', function () {
+    it('is correctly detected in first argument position', async function () {
+      expect(await this.math.$min(min, max)).to.be.bignumber.equal(min);
+    });
+
+    it('is correctly detected in second argument position', async function () {
+      expect(await this.math.$min(max, min)).to.be.bignumber.equal(min);
+    });
+  });
+
+  describe('average', function () {
+    function bnAverage(a, b) {
+      return a.add(b).divn(2);
+    }
+
+    it('is correctly calculated with various input', async function () {
+      const valuesX = [
+        new BN('0'),
+        new BN('3'),
+        new BN('-3'),
+        new BN('4'),
+        new BN('-4'),
+        new BN('57417'),
+        new BN('-57417'),
+        new BN('42304'),
+        new BN('-42304'),
+        MIN_INT256,
+        MAX_INT256,
+      ];
+
+      const valuesY = [
+        new BN('0'),
+        new BN('5'),
+        new BN('-5'),
+        new BN('2'),
+        new BN('-2'),
+        new BN('57417'),
+        new BN('-57417'),
+        new BN('42304'),
+        new BN('-42304'),
+        MIN_INT256,
+        MAX_INT256,
+      ];
+
+      for (const x of valuesX) {
+        for (const y of valuesY) {
+          expect(await this.math.$average(x, y)).to.be.bignumber.equal(
+            bnAverage(x, y),
+            `Bad result for average(${x}, ${y})`,
+          );
+        }
+      }
+    });
+  });
+
+  describe('abs', function () {
+    for (const n of [
+      MIN_INT256,
+      MIN_INT256.addn(1),
+      new BN('-1'),
+      new BN('0'),
+      new BN('1'),
+      MAX_INT256.subn(1),
+      MAX_INT256,
+    ]) {
+      it(`correctly computes the absolute value of ${n}`, async function () {
+        expect(await this.math.$abs(n)).to.be.bignumber.equal(n.abs());
+      });
+    }
+  });
+});