feat: add env_str to snippet_client_v2.Config to allow am instrument command prefix (fixes #1004)

[devimano2011]

Fixes #1004

Problem

Users who need to prepend environment variables or command wrappers (e.g. ENV_VAR=value or a wrapper command) to the am instrument command in snippet_client_v2 had no way to do so.

Solution

Add an env_str field to snippet_client_v2.Config that, when set, is prepended to the am instrument command. This allows users to:

• Set environment variables: config.env_str = 'MY_VAR=value'
• • Use command wrappers: config.env_str = 'wrapper_cmd'

Changes

• Added env_str: str = '' field to the Config dataclass with documentation
• • Updated _LAUNCH_CMD template to support {env_str} prefix
• • Pass env_str value when building the launch command in _start_server()

Usage

config = snippet_client_v2.Config(env_str='MY_VAR=hello')
ad.load_snippet('maps', 'com.example.maps', config=config)

[mhaoli]

Please add unit tests for the changes.

[devimano2011]

Hi @mhaoli, unit tests have been added as requested in commit d2dd8fa.

The following 6 tests were added to tests/mobly/controllers/android_device_lib/snippet_client_v2_test.py:

• test_config_env_str_default_is_empty_string — verifies Config.env_str defaults to ''
• • test_config_env_str_can_be_set — verifies the field stores an assigned value correctly
• • test_start_server_with_env_str — verifies a non-empty env_str is prepended to the am instrument command
• • test_start_server_without_env_str_no_extra_space — verifies no extra whitespace is injected when env_str is empty
• • test_start_server_with_env_str_has_trailing_space — verifies exactly one space separates env_str from am instrument
• • test_start_server_with_multiple_env_vars — verifies multiple space-separated env vars are preserved
    Please let me know if any further changes are needed. Thanks!

[mhaoli]

Why are you adding unit tests under the if __name__ == '__main__' block?

[devimano2011]

Good catch @mhaoli! The tests were accidentally placed inside the if __name__ == '__main__' block. Fixed in the latest commit — all 6 tests are now correctly at class level. Apologies for the error!