function AssertionError(options) {
            options = options || {};
            this.name = 'AssertionError';
            this.message = options.message;
            this.actual = options.actual;
            this.expected = options.expected;
            this.operator = options.operator;
            const stackStartFunction = options.stackStartFunction || fail;

            if (Error.captureStackTrace) {
                Error.captureStackTrace(this, stackStartFunction);
            }
        }
# .closeTo(expected, delta)

Assert that actual is equal to +/- delta.

     expect(1.5).to.be.closeTo(1, 0.5);

@name closeTo
@param {Number} expected
@param {Number} delta
@api public