Fix #433: allow test_context() for sink-less (non-yielding) agents

[wbarnha]

What

Agent.test_context() wraps the agent in an AgentTestWrapper that unconditionally added an internal "results" sink. For an agent that never yields, that sink tripped _prepare_actor's guard:

faust.exceptions.ImproperlyConfigured: Agent must yield to use sinks

…which is raised at agent startup, so test_context() could not be used to unit-test sink-less agents at all — you had to add a throwaway yield just to make the harness work.

Fixes #433.

How

Detect whether the wrapped agent actually yields, via inspect.isasyncgenfunction(self.fun):

• Yielding agent — unchanged: attach the results sink (_on_value_processed), which records yielded values and wakes put(wait=True).
• Non-yielding agent — skip the sink (so the ImproperlyConfigured guard is not tripped) and instead attach a stream processor. The processor records each incoming value into results and notifies new_value_processed, so put(wait=True) still returns after the value is processed. The processor returns the value unchanged, leaving the agent's own iteration untouched.

This mirrors the approach a maintainer suggested on the issue ("check in test_context if it is already yielding and if not … [handle it another way]"), without requiring the user to change their agent.

Test

Added test_context__sinkless_agent in tests/unit/agents/test_agent.py (alongside the existing test_context_calls_sink): defines a non-yielding agent, enters test_context(), await agent.put("hello"), and asserts the value was processed and recorded — a case that previously raised ImproperlyConfigured at startup. Full tests/unit/agents/test_agent.py passes (73 passed, 1 skipped).

🤖 Generated with Claude Code

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Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.15%. Comparing base (3073eb9) to head (de309e0).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #699   +/-   ##
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  Coverage   94.14%   94.15%           
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  Files         104      104           
  Lines       11136    11137    +1     
  Branches     1201     1201           
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+ Hits        10484    10486    +2     
+ Misses        551      550    -1     
  Partials      101      101           

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