Added makeInterfaceId tests. (#1530)

contracts/mocks/OwnableInterfaceId.sol

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+pragma solidity ^0.4.24;
+
+import "../ownership/Ownable.sol";
+
+/**
+ * @title Ownable interface id calculator.
+ * @dev See the EIP165 specification for more information:
+ * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-165.md#specification
+ */
+contract OwnableInterfaceId {
+    function getInterfaceId() public pure returns (bytes4) {
+        Ownable i;
+        return i.owner.selector ^ i.isOwner.selector ^ i.renounceOwnership.selector ^ i.transferOwnership.selector;
+    }
+}

test/helpers/test/makeInterfaceId.test.js

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+const { makeInterfaceId } = require('../makeInterfaceId');
+
+const OwnableInterfaceId = artifacts.require('OwnableInterfaceId');
+
+require('chai')
+  .should();
+
+describe('makeInterfaceId', function () {
+  it('calculates the EIP165 interface id from function signatures', async function () {
+    const calculator = await OwnableInterfaceId.new();
+    const ownableId = await calculator.getInterfaceId();
+
+    makeInterfaceId([
+      'owner()',
+      'isOwner()',
+      'renounceOwnership()',
+      'transferOwnership(address)',
+    ]).should.equal(ownableId);
+  });
+});