[test] Fix race condition when accessing command buffer output

[liran-funaro]

Type of change

• Bug fix
• Test update

Description

Root cause: The test was experiencing a race condition when accessing command output buffers. In UnitTestRunner, the command execution runs in a goroutine that continuously writes output to bytes.Buffer instances (cmdStdOut and cmdStdErr), while simultaneously another goroutine in assert.Eventually reads from these buffers via cmdStdOut.String() to check for expected output. Since bytes.Buffer is not thread-safe for concurrent read/write operations, this caused data races detected by the race detector when multiple goroutines accessed the buffer simultaneously.

Related issues

• discovered by [CI] Enable race detection for unit tests in CI #442

[coveralls]

coverage: 90.389% (+0.1%) from 90.284%
when pulling a91b370 on liran-funaro:buffer-race
into 355e2a9 on hyperledger:main.

[cendhu]

LGTM