Heater Left Plugged In Minus Water - Request For Advice

I've just undertaken the weekly tank maintenance and, owing to mind distracted by other matters, unfortunately left the heater plugged in throughout ie for ~an hour with water at 50% volume.   
   
My spare heater is one which, a year or two ago, was left plugged in for a much shorter timeframe before I realised and salvaged the situation.  It got downgraded from main heater to spare heater, as I couldn't be certain I'd not broken it.

Thoughts: Test out in bucket of cold water, essentially 'forcing' it to auto-switch on and monitor with thermometer that it doesn't go beyond the thermostat-set temp of 26'C.  Buy a new heater if broken.
Question: Would the above suffice, or is there still a risk that I've broken the heater?  I don't want any risk of the tank temperature dropping during the night, the heater auto-switching on and then 'cooking' the fish during the night.

...Maybe I should just buy a new heater anyway, for peace of mind, rather than be on tenterhooks for weeks...

Thanks, Sue.  It's a glass one.  It raised the temperature correctly to the thermostat-set temp, then clicked off just after reaching that as I was watching it.  Phew.  I've also checked it throughly for cracks, and very fortunately don't see any.

I'm currently testing out the older/spare heater.  I forgot that its pilot light doesn't work but I've shoved its thermostat-set temp up to its maximum of 32'C to see if it raises the temperature on the thermometer reading in the bucket of water accordingly and doesn't go beyond that.  However, I also forgot that it has some slight condensation which hasn't dried out in all the time of lack of use - see attached photo.  Would the latter mean it's broken, its function simply 'compromised'/inefficient, or possibly neither (esp if it passes the above test)?

Great - thanks.

The 'spare heater' testing is complete, and a useful reminder that the temperature goes up to 3-4'C above its pre-set temperature, irrespective of what it's set at - a fact I'd completely forgotten.  (I used to assume the tank temperature was always higher due to the summer / good insulation / central heating, but now realise that's not the case - the current thermometer has always been consistent with the pre-set heater temperature even with summer heatwaves and minimising central heating use in winter in recent years.)  I have now labelled the plug accordingly with a reminder, and with a warning not to put hands in tank if using it.