Why does the following test give me a TypeError: expected numeric error:
it { expect(DateTime.now).to be_within(1.second).of Time.zone.now }
but this test does not?
it { expect(DateTime.now).to be_within(1.second).of Time.zone.now.to_datetime }
1
You can easily reproduce this outside of RSpec (and outside of ruby-on-rails)
DateTime.now - Time.now
#=> expected numeric (TypeError)
Had you posted the full stack trace it would have shown the error occurred in Date#minus_without_duration (added by ActiveSupport), which is simply an alias for Date#-.
Ruby’s Date#- method states:
Returns the difference between the two dates if the other is a date object. If the other is a numeric value, returns a date object pointing
otherdays before self. If the other is a fractional number, assumes its precision is at most nanosecond.
Time (or more accurately in this case ActiveSupport::TimeWithZone) is not a Date nor is it a Numeric, thus the TypeError.
When you convert it to a DateTime, a DateTime is a Date, so the method functions appropriately.
In order for the comparison to work appropriate just make sure the 2 objects are #- compatible (and technically that #- returns a Numeric value or some other object that responds to abs [see below]).
In your case you can accomplish this a number of ways including Time#to_datetime (as shown), DateTime#in_time_zone, DateTime#to_time, etc.
How this relates to RSpec::Matchers::BuiltIn::BeWithin:
The syntax in this case is expect(actual).to be_within(tolerance).of(expected)
The matcher processes a match as: (Source)
numeric? && (@actual - @expected).abs <= @tolerance
Which in this case equates to
actual = DateTime.now
tolerance = 1
expected = Time.zone.now
if actual.respond_to?(:-)
difference = actual - expected # Error occurs here
difference.abs <= tolerance
else
false
end