Add error message testing arm

[sigilante]

Target tested code:

++  fail
  |=  *
  ~|(%an-error-message !!)

Usage in a test thread:

++  test-failure
    %+  expect-fail-message
      %an-error-message                                                         
    |.  (fail:main ~)

A recursive +find could make this less cumbersome.

[jackfoxy]

This works for "vanilla" test failure

++  test-fail-time-create-ns-lt-schema
  =|  run=@ud
  =/  my-cmd  "CREATE NAMESPACE ns1 as of ~2023.7.9..22.35.33..7e90"
  %+  expect-fail-message
      'namespace %ns1 as-of schema time out of order'
      |.  %-  process-cmds 
              :+  gen3-dbs
                  (bowl [run ~2031.1.1])
                  (parse:parse(default-database 'db1') my-cmd)

But not testing a poke

++  test-fail-time-create-ns-lt-schema
  =|  run=@ud
  =^  mov1  agent  
    %:  ~(on-poke agent (bowl [run ~2000.1.1]))
        %obelisk-action
        !>  :-  %tape-create-db 
                "CREATE DATABASE db1 as of ~2023.7.9..22.35.35..7e90"
    ==
  =.  run  +(run)
  %+  expect-fail-message
      'namespace %ns1 as-of schema time out of order'
      |.  %:  ~(on-poke agent (bowl [run ~2000.1.2]))
              %obelisk-action
              !>  :-  %tape-create-db
                      "CREATE NAMESPACE ns1 as of ~2023.7.9..22.35.34..7e90"
          ==

[sigilante]

An agent is going to route through ++on-fail. Offhand I think you'd have to test whatever state change or result that ++on-fail produces.

[jackfoxy]

Yet changing the expect-fail-message step to expect-eq fails with a stack trace containing the expected message.