Plenty of candidates do not finish. Here is exactly what that means.

Are you charged?
It depends on how far they got.
| They | Charged? |
|---|---|
| Were invited and never registered | No |
| Registered and started nothing | No |
| Started a test and never submitted it | No |
| Submitted at least one test, then stopped | Yes, once |
The charge lands on the first completed test, not on finishing the assessment. Someone who submits test one and abandons test two counts as a candidate, the same as someone who did everything.
Full detail in when a candidate is charged.
What you can see
Everything they completed. A candidate part way through has a readable result for each submitted test, an overall score across those tests, and the full answer-by-answer view for each.
Their report says how many tests of how many have been submitted and that the full report follows when the rest arrive. Tests they have not taken show as not taken rather than as zero.
Should you read a partial result?
Carefully. A partial assessment is real evidence about the tests they did take and no evidence at all about the rest. Comparing their overall score against someone who completed everything is comparing different things: the averages are taken over different tests.
If you are ranking, rank the completed candidates and treat partial ones separately.
What to do about a partial result
Send them a reminder. One click from their row, and it reaches them with a working link. Their finished tests stay finished. See send a reminder or resend an invitation.
Check the deadline. If it has passed, their link will not reopen the assessment. Extend it if you want them back in.
Ask what happened. Candidates stop for ordinary reasons: a connection dropped, the clock ran out, a child needed something. The candidate help centre covers all of those, and pointing them at it is often the whole fix.
Reducing partial completions
Drop-out is mostly a function of length. See how many tests to include and put the test you most want to read first.