Detect NeoPixel status
An idea: The pixels pass the data through, removing one message, each time.
You could write to the string as though it has one more pixel.
Connect the data line from the far end back to the Arduino, and check that you get one message out the other end. This would confirm that the string is working.

Note that the first line on the Adafruit site says "There are some things to watch for. These LED's use about 9.5 Watts max (~2 Amps @ 5V) per meter"  So you will quickly run into trouble powering them from USB. You will need to protect your circuit against the neopixel strip!