testing: show extra information on failure

[andrewliebenow]

No description provided.

[andrewliebenow]

Old:

---- tr::tr_octal_above_one_byte_value stdout ----
thread 'tr::tr_octal_above_one_byte_value' panicked at plib/src/testing.rs:85:5:
assertion `left == right` failed
  left: "(Ł)"
 right: "Ł)"
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

New:

---- tr::tr_octal_above_one_byte_value stdout ----
thread 'tr::tr_octal_above_one_byte_value' panicked at plib/src/testing.rs:229:9:
------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------
Test failed with 2 total failure types
--------------------------------------------------------------------------------

Command executed
--------------------------------------------------------------------------------
tr -d \501
--------------------------------------------------------------------------------

Failure 1 of 2: stdout differs from what was expected
--------------------------------------------------------------------------------

Actual
--------------------------------------------------------------------------------
(Ł)
--------------------------------------------------------------------------------

Expected
--------------------------------------------------------------------------------
Ł)
--------------------------------------------------------------------------------

Failure 2 of 2: stderr differs from what was expected
--------------------------------------------------------------------------------

Actual
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

Expected
--------------------------------------------------------------------------------
tr: warning: the ambiguous octal escape \501 is being interpreted as the 2-byte sequence \050, 1

--------------------------------------------------------------------------------


stderr, for diagnosing failure
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------

note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[andrewliebenow]

The new format might look a bit verbose, but I've repeatedly run up against:

1. Not remembering what left/right correspond to (actual/expected)
2. Not knowing if the comparison is in stdout or stderr
3. Not having access to any additional information beyond that which is provided by the first failed assertion

[Copilot]

Pull Request Overview

This PR enhances the test failure reporting by displaying additional information when tests do not pass as expected. The changes include improved formatting with consistent markers, detailed messages for differences in stdout, stderr, and exit code, and a consolidated failure summary report.

[Copilot]

The code computes a truncated version of stderr as 'stderr_truncated' but later prints the full 'stderr_cow' instead. Consider printing 'stderr_truncated' in the failure message when its length differs from 'stderr_cow'.

Suggested change

	{stderr_cow}
	{}