Expand unit test coverage from 40% to 80%

[kcenon]

What

Drive network_system line coverage from 65.1% to 80% and branch coverage from 31.1% to 70% (measured on develop, 2026-04-20, coverage run 24659295053). The remaining gap is concentrated in protocol implementation files whose existing tests cover happy paths but not error/boundary branches.

History note (2026-04-16): This epic originally targeted ~40% coverage with 60+ untested modules. That premise was stale — sub-issues #982, #983, #984, #985 were closed after auditing the existing tests/unit/ tree (~112 test files, ~44,200 LOC, ~2,989 GTEST cases). The real gap is that many existing tests do not exercise error paths, branch combinations, and edge cases in the protocol code.

Progress note (2026-04-22): Step 1 (coverage measurement fix) is complete via #986, #987, #989. Step 2 (narrow test expansion) is in progress with #991, #992, #993, #990, #994 closed.

Why

• 80% line coverage is the explicit v1.0 target for this project (see Prepare network_system for v1.0 release #964 dependency)
• Ecosystem peers (database_system: 87%, thread_system: 72%) are above network_system
• Result<T> migration and API stabilization increase regression risk on low-coverage protocol code
• Branch coverage at 31.1% means ~25,000 branches go untested — many are error paths whose failure modes are not verified

Where

Current baseline (post Step 1)

Metric	Value	Target	Gap
Line coverage	65.1% (15045 / 23099)	80%	~3,434 lines
Branch coverage	31.1% (11370 / 36532)	70%	~14,202 branches

Coverage workflow configuration (verified current)

.github/workflows/coverage.yml now builds with:

-DBUILD_WITH_COMMON_SYSTEM=ON
-DBUILD_WITH_LOGGER_SYSTEM=ON
-DBUILD_WITH_THREAD_SYSTEM=ON
-DBUILD_WITH_CONTAINER_SYSTEM=ON
-DBUILD_MESSAGING_BRIDGE=ON

Branch coverage is captured via lcov --rc lcov_branch_coverage=1 and rendered with genhtml --branch-coverage.

Worst-coverage implementation files (pre-Step-1 snapshot, needs re-measurement)

These file-level numbers were collected from the 2026-04-13 run before the BUILD_WITH_* flags were enabled. Re-measurement with the current workflow is pending. Already-addressed files are marked.

• protocols/quic/frame.cpp — 15.0% of 600 lines (file is now 1203 lines; existing tests cover build/parse happy paths only)
• internal/http_parser.cpp — 6.0% of 348 lines
• tracing/exporters.cpp — 7.4% of 340 lines
• protocols/quic/crypto.cpp — 12.1% of 313 lines (addressed by test: expand coverage for src/protocols/quic/crypto.cpp #993 / PR test(quic): add extended coverage tests for crypto module #1002)
• protocols/http2/frame.cpp — 12.9% of 310 lines
• protocols/quic/transport_params.cpp — 4.2% of 289 lines
• protocols/http2/hpack.cpp — 13.5% of 244 lines
• core/unified_session_manager.cpp — 26.1% of 222 lines
• protocols/quic/packet.cpp — 11.0% of 210 lines
• protocols/quic/loss_detector.cpp — 7.6% of 210 lines
• tcp_socket.cpp — 14.8% of 209 lines
• internal/utils/compression_pipeline.cpp — 12.5% of 200 lines
• internal/http_error.cpp — 3.2% of 190 lines

How

Step 1 — Fix the measurement (DONE)

• Modify .github/workflows/coverage.yml to enable all BUILD_WITH_* flags — ci(coverage): enable full-ecosystem coverage build #987, ci(coverage): enable messaging_bridge in coverage build #989
• Enable branch coverage (lcov --rc lcov_branch_coverage=1) — ci(coverage): enable branch coverage and manual run #986
• Re-run on main/develop and record new baseline — 65.1% lines / 31.1% branches captured 2026-04-20

Step 2 — Narrowly-scoped test issues (IN PROGRESS)

For each remaining file still under 70% with >100 lines, open a single-file test expansion issue (size/S or size/M). Do not open XL epics.

Closed sub-issues (folded test expansion):

• test: expand coverage for src/protocols/http2/http2_client.cpp #991 — http2/http2_client.cpp
• test: expand coverage for src/protocols/http2/http2_server.cpp #992 — http2/http2_server.cpp
• test: expand coverage for src/protocols/quic/crypto.cpp #993 — quic/crypto.cpp
• test: expand coverage for src/protocols/quic/connection.cpp #990 — quic/connection.cpp
• test: expand coverage for src/protocols/grpc/client.cpp #994 — grpc/client.cpp

Open / upcoming sub-issues: see issues labeled Part of #953.

Step 3 — Close this epic when the acceptance criteria below are met

Acceptance Criteria

• Coverage workflow rebuilt with all BUILD_WITH_* options enabled
• Branch coverage captured (not "no data found")
• Re-measured line coverage recorded on this issue (65.1% as of 2026-04-20)
• Overall line coverage >= 80% (codecov)
• Branch coverage >= 70%
• All narrow test-expansion follow-ups are closed
• All tests pass on Ubuntu/macOS/Windows CI
• All sanitizer builds (ASAN, TSAN, UBSAN) pass

Dependencies

• Related: Prepare network_system for v1.0 release #964 (v1.0 readiness — this epic's completion is a v1.0 prerequisite)
• Closed sub-issues (folded into rebaseline): Add unit tests for QUIC protocol suite (18+ modules) #982, Add unit tests for facade and adapter layers (22 modules) #983, Add unit tests for HTTP/2, session, and tracing modules (10 modules) #984, Add unit tests for UDP messaging and integration modules (10 modules) #985
• Test expansion sub-issues completed so far: test: expand coverage for src/protocols/quic/connection.cpp #990, test: expand coverage for src/protocols/http2/http2_client.cpp #991, test: expand coverage for src/protocols/http2/http2_server.cpp #992, test: expand coverage for src/protocols/quic/crypto.cpp #993, test: expand coverage for src/protocols/grpc/client.cpp #994

---

Update (2026-04-26)

Re-measurement on develop @ 05c1b7b

Coverage workflow run 24947193873:

Metric	Baseline 2026-04-20	Current 2026-04-26	Target	Gap
Line coverage	65.10% (15,045 / 23,099)	66.59% (15,382 / 23,099)	80%	-13.41%p
Branch coverage	31.13% (11,370 / 36,532)	32.95% (12,039 / 36,532)	70%	-37.05%p

The denominator is unchanged — sub-issues #1020-#1034 added tests but did not modify the source LOC pool. Net delta: line +337 hit / branch +669 hit.

Step 2 sub-issues closed in this batch (2026-04-24 to 2026-04-26)

#1020, #1021, #1022 (closed as not-planned), #1023, #1024, #1025, #1026, #1027, #1028, #1029, #1030, #1031, #1032, #1033, #1034 — all merged via PRs #1023-style follow-up to #1047.

Where section is now obsolete

The pre-Step-1 file list above (e.g. protocols/quic/frame.cpp 15.0%, protocols/http2/hpack.cpp 13.5%) has been fully addressed. New worst-coverage files identified from the 2026-04-26 measurement:

Priority	File	LOC	Line%	Branch%	Note
1	protocols/http2/http2_client.cpp	576	18.8%	9.9%	Follow-up to #991 (happy paths only)
2	protocols/grpc/client.cpp	482	22.6%	9.5%	Follow-up to #994
3	protocols/http2/http2_server.cpp	554	38.3%	19.4%	Follow-up to #992
4	internal/quic_socket.cpp	439	43.7%	21.3%	New target
5	experimental/quic_server.cpp	378	43.7%	17.5%	New target
6	http/websocket_server.cpp	308	39.9%	19.7%	New target

Next steps (Step 2 continues)

• Open narrow test-expansion sub-issues for the six files above (Part of #953).
• Re-measure after each merge; expect ~80% line coverage to require ~3,000 additional hit lines.
• Branch coverage target (70%) is the larger gap and may require explicit error-path tests beyond what unit tests typically cover — consider integration-level fuzzing if line target is reached but branch is not.

[kcenon]

Sub-Issues

• Add unit tests for QUIC protocol suite #954 — Add unit tests for QUIC protocol suite (size/L)
• Add unit tests for facade and adapter layers #955 — Add unit tests for facade and adapter layers (size/L)
• Add unit tests for HTTP/2, session, and tracing modules #956 — Add unit tests for HTTP/2, session, and tracing modules (size/M)

Related

• Complete Result<T> migration in bridge/adapter implementations #957 — Complete Result migration in bridge/adapter implementations
• Track ecosystem-wide v1.0 API stabilization readiness common_system#639 — Ecosystem v1.0 API stabilization tracking
• Exclude .key files from git and regenerate in CI pacs_system#1092 — Exclude .key files from git

[kcenon]

Progress Update

3 of 4 sub-issues completed:

• Add unit tests for QUIC protocol suite #954 Add unit tests for QUIC protocol suite — Closed via PR test(quic): add unit tests for 9 QUIC protocol modules #959
• Add unit tests for facade and adapter layers #955 Add unit tests for facade and adapter layers — Closed via PR test(adapters): add unit tests for 13 protocol adapter modules #960
• Add unit tests for HTTP/2, session, and tracing modules #956 Add unit tests for HTTP/2, session, and tracing modules — Closed via PR test(http2,session): add HPACK RFC 7541 and session lifecycle tests #961
• Add unit tests for UDP messaging and integration modules (not yet created as issue)

Additionally, #957 (Result migration) was completed via PR #962, improving error handling consistency across all bridge/adapter code.

Summary of new test coverage added

PR	Test Files	Lines Added
#959	9 QUIC unit tests	+4,002
#960	13 adapter unit tests	+1,502
#961	HPACK RFC 7541 + session lifecycle	+1,289
Total	24 new test files	+6,793 lines