export function supportProperHex(Assertion: Chai.AssertionStatic) {
  Assertion.addMethod('properHex', function (this: any, length: number) {
    const subject = this._obj;
    const regexp = new RegExp(`^0x[0-9-a-fA-F]{${length}}$`);
    this.assert(regexp.test(subject),
      `Expected "${subject}" to be a proper hex of length ${length}`,
      `Expected "${subject}" not to be a proper hex of length ${length}, but it was`,
      'proper address (eg.: 0x1234567890123456789012345678901234567890)',
      subject);
  });
}