[Test Improver] test: add unit tests for AgentsCompiler (65%→82% coverage)

[danielmeppiel]

🤖 Test Improver – automated AI assistant

Goal & Rationale

src/apm_cli/compilation/agents_compiler.py is the main orchestrator for all AGENTS.md/CLAUDE.md compilation. At 65% coverage, many important error-handling and edge-case branches were untested, including:

• Config loading from apm.yml (legacy single_file flag, placement settings, source attribution)
• Exception paths that produce silent fallbacks instead of crashes
• File-write error handling for both single-file and distributed modes
• The _write_distributed_file() method (0% covered)

Approach

Added 34 focused unit tests in tests/unit/compilation/test_agents_compiler_coverage.py, complementing the existing test_compilation.py:

Test class	Tests	What it covers
TestCompilationConfigFromApmYmlAdditional	10	target, strategy, legacy single_file, min_instructions_per_file, source_attribution, exception fallback, no-file defaults
TestCompilationConfigPostInit	2	single_agents → strategy, exclude=None init
TestAgentsCompilerCompileException	2	Exception → failure result; local_only uses basic discover
TestValidatePrimitivesErrors	4	Primitive errors → warnings; outside-base-dir path; link errors
TestWriteOutputFile	1	OSError adds compiler error
TestWriteDistributedFile	4	Dir creation, no-constitution, injection failure fallback, OSError re-raise
TestGenerateSummaries	4	Relative and absolute-path cases for both summary methods
TestMergeResults	5	Empty list, single pass-through, two-result merge, failure propagation
TestCompileAgentsMdFunction	2	Error path raises RuntimeError; success returns content

Coverage Impact

Module	Before	After
agents_compiler.py	65%	82%

Remaining uncovered lines (264-275, 278-280, 294-295, 312-333, 436-437, 467-468, 472-473, 501, 503, 517-518, 759-774, 783-801) are inside _compile_distributed() and _compile_claude_md() display/formatting paths that require a full distributed compiler stack — not targeted in this PR.

Test Status

34 passed in 0.27s   (new tests alone)
964 passed, 1 failed (full suite, pre-existing ANSI failure in test_install_command.py)

The pre-existing failure (test_install_no_apm_yml_no_packages_shows_helpful_error) is unrelated to this change — it's caused by Rich-formatted output containing ANSI escape codes that the test asserts against plain text.

Reproducibility

uv sync --extra dev
uv run pytest tests/unit/compilation/test_agents_compiler_coverage.py -v
uv run pytest tests/unit/compilation/ --cov=apm_cli.compilation.agents_compiler --cov-report=term-missing

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