CI failure due to dropped trailing zero on timestamp

[philrz]

Since the merge of #1792, we've had intermittent failures in the Brim CI. I created a branch and triggered the CI several times and found it failed 6 out of 10 times. I think I can see the pattern of what's wrong.

The failures look like this:

FAIL app/search/flows/viewer-search.test.ts
  ● a normal response › zealot gets the request

    expect(received).toEqual(expected) // deep equality

    Expected: "from '1' | ts >= 2021-09-15T01:15:19.060Z | ts <= 1970-01-01T00:00:00.001Z | dns query | head 500"
    Received: "from '1' | ts >= 2021-09-15T01:15:19.06Z | ts <= 1970-01-01T00:00:00.001Z | dns query | head 500"

Peeking at the code at https://github.com/brimdata/brim/blob/0dcf10c452efba1de841a512b38dc1c424f01e25/app/search/flows/viewer-search.test.ts#L62 we see the from value starts life as a response from new Date(), which returns the current date and time, and hence is going to vary on each run, which explains the non-determinism. While I don't claim to understand all aspects of the test code, assuming the "Received" value is coming from the backend in some way, we can see by hitting Zed directly how it drops trailing zeros like this.

$ zq -version
Version: v0.30.0-5-g5c4868de

$ echo '{mytime: 2021-09-15T01:15:19.060Z}' | zq -
{mytime:2021-09-15T01:15:19.06Z}

I'm guessing that for the runs that succeed there's no trailing zero in the current timestamp.