Add smoke test for google_set_multiqueue

[copybara-service]

Add smoke test for google_set_multiqueue

The test runs against input cases in test_data/, which are expected to
contain:

• in/, the test inputs
  • commands.json, exact command invocations to fake using fake_bin.
  • fs.textproto, a representation of the filesystem to simulate for
    the test.
  • mds.json, the set of all possible Metadata Server queries which
    can be faked by fake_mds.
• want/, the test expectations
  • commands, a simple text file which contains exact command
    invocations which were expected to be sent to fake_bin by the
    script under test. Commands
    listed here are requred, but additional commands are accepted.
  • fs.textproto, a representation of files on the disk which we
    expect to be in a specific state after the script runs.
    Similar to commands, extra writes are ignored.

At runtime, the test:

• Starts an instance of fake_mds, referencing mds.json.
  • The ephemeral port which the server bound to is printed to stdout
• Sets up a directory for fake binaries.
  • Most of these are symlinks to fake_bin, which behaves as described
    above.
  • We additionally inject a link to curl, if and only if
    --curl_path is specified as an argument to the test. Otherwise,
    the script under test will implicitly use curl from the host
    system if it exists. This allows testing specific versions of curl,
    and is provided for compatibility with Google's internal tooling.
• Sets some environment variables to configure the test tools and to
  inject the fake filesystem / metadata server into the script under
  test.
• Runs the script under test.
• Asserts that expected modifications to the filesystem, and specific
  CLI commands were called, as described above.

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: copybara-service[bot]

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment