AutoTest connects successfully to a network but fails the Connection Test
Part of the AutoTest’s Connection Test for a network includes measurements from a passive channel scan that is performed prior to connecting to a network. These measurements include Network Coverage and Co-channel Interference. If either of these fail to meet a “Pass” threshold, then the Connection test will fail. Thresholds for these tests can be adjusted in Settings / Thresholds.
 
AutoTest connects successfully to a network but Network Coverage for that network shows 0 APs
AutoTest’s Network Coverage test counts APs above a signal level threshold. It is possible that your network has 0 APs above that threshold, but at least 1 AP that is still strong enough to connect to. Thresholds for this test can be adjusted in Settings / Thresholds.

AutoTest Adjancent Channel Interference (ACI)
The ACI test reports, for each channel on which there is at least one AP, how many APs are on other channels that overlap. This is different than Co-channel Interference which reports how many APs are on the same channel. For example, for channel 6, the ACI test would count APs on adjacent overlapping channels: 4, 5, 7, 8. But would not count APs on channel 6 since these are counted in the Co-channel Interference test. The ACI test also takes into account 802.11n 40MHz channels in the 2.4 GHz band. The ACI test operates only in the 2.4 GHz band since the sequential channels in the 5 GHz band do not overlap.