Fast, hardware-free unit tests for pure and host-simulated logic, run with GoogleTest through PlatformIO. The native environment runs every suite except the KISS modem; native_kiss_modem builds that suite with its separate source filter. Hardware, real radio, AsyncTCP, Wi-Fi/MQTT, and SoftAP behavior still require integration or target testing; see "Local testing without hardware" in MQTT_IMPLEMENTATION.md.

Running

pio test -e native                      # all suites except KISS modem
pio test -e native_kiss_modem           # KISS modem suite
pio test -e native -f test_webconfig_keys   # a single suite
python3 test/test_radio_receive_contract.py # real CAD/re-arm/calibration/mode-watchdog methods
python3 test/test_sx126x_receive_mode.py    # pinned RadioLib SPI transport/status-byte regression
python3 test/test_firmware_ram.py        # every firmware hook, ELF heaps, reservations, RAM report binding
python3 test/test_indicator_display_profile.py  # Indicator RAM/scale contract
python3 test/test_indicator_render_profile.py   # four-mode Indicator canvas matrix/fallback contract
python3 test/test_indicator_exclusive_transport.py  # Indicator secondary-transport ownership contract
python3 test/test_companion_transport_selector.py  # Indicator transport-selector touch/UI contract
python3 test/test_color_theme.py                # shared color-display dark-palette contract
python3 test/test_indicator_font_recovery.py  # Indicator TLS/SD font recovery contract
python3 test/test_companion_terminal_profile.py  # Companion CLI capability gates
python3 test/test_bluetooth_mac_contract.py     # MAC policies, separate stealth flag and BLE backend integration
python3 test/test_companion_settings_persistence_contract.py  # Atomic settings and appended Bluetooth fields
python3 test/test_webconfig_ui.py              # Web controls, reboot handling and generated-page consistency
python3 test/test_webconfig_ui_runtime.py      # Real Chromium, including independent stealth toggle
python3 test/test_nrf52_uf2reset_cli.py          # all nRF52 text-CLI reset dispatchers
python3 test/test_nrf52_bootloader_version.py -v  # real C++ version reader, metadata and firmware wiring
python3 test/test_client_login_profile_contract.py  # ACL login ordering/role contract
python3 test/test_client_acl_spiffs.py          # Actual ACL: first login, replay/reboot, failed storage
python3 test/test_replay_reset_command.py       # Strict full keys and one-use recovery confirmations
python3 test/test_replay_reset_integration.py   # Actual repeater handler: USB/LoRa permissions and persistence ordering
python3 test/test_regular_file_reads.py         # SPIFFS phantom directories, listings, log HTTP status
python3 test/test_esp32_full_partition.py       # Full partition-preservation policy
python3 test/test_esp32_dram.py                 # Classic ESP32 static limits and cached-image build gates
python3 test/test_esp32_usb_serial_hygiene.py   # Single-TTY diagnostics/NVS contract
python3 test/test_esp32_usb_sleep.py            # USB/logging sleep guards, G3 button wake and two-minute hold/rollover
python3 test/test_logging_sleep_contract.py    # USB enable examples and real Repeater/Room MQTT sleep gates
python3 test/test_t096_full_memory.py          # Full profile, shared queue wraparound, heap reserve and sensor OOM
python3 test/test_nrf52_ble_startup.py          # Real task wrapper/BLE startup with worker and GATT failures
python3 test/test_shared_mota_queue.py          # Real mOTA transfers, BLE stop/disconnect, queue loans and policy retention
python3 test/test_esp32_tinyusb_role_hygiene.py # G2/room USB write coverage and bounded-list contracts
python3 test/test_esp32_tinyusb_cooperative_output.py # Real role dump/list pumps with host C++ stubs
python3 test/test_esp32_tinyusb_nonblocking.py # Native CDC stalled-host/64-byte-FIFO simulation (C++17 compiler)
python3 test/test_esp32_tinyusb_role_hygiene.py # Repeater/room nonblocking console and paced large replies
python3 test/test_esp32_tinyusb_cooperative_output.py # Real role pumps: large logs/listings, EOF, backpressure
python3 test/test_temp_radio_reply_delivery_contract.py  # TempRadio ACK path/barrier integration
python3 test/test_repeater_radio_timing_integration.py  # Real scheduler, watchdog, hourly/flood adverts and restoration
python3 test/test_tls_download_clock_gates.py   # Fresh-NTP/TLS download integration contract

The WebConfig browser suite skips if no Chromium-family browser is available. With a sandboxed browser that cannot read /tmp, set TMPDIR to a writable directory visible to that browser before running it. The Bluetooth settings contracts and WebConfig suites also run in the unit-test GitHub workflow.

The bootloader-version regression compiles the production reader with a C++17 g++ (or CXX) compiler. Its offline cases include the MeshTower V2 SD 2.4.6 missing-UF2-text failure, OTAFIX metadata versus cached base-version precedence, stock/vendor/preview strings, bounds, truncation, invalid CRCs and malformed metadata. A separate CI job also downloads the pinned OTAFIX 2.4.6 release archive, verifies its SHA-256 and all 17 signed packages, and feeds their actual bootloader payloads through the same C++ reader. No radio is accessed or flashed. To repeat the release test locally, install Python cryptography and set MESHCORE_BOOTLOADER_MOTA_ZIP to the downloaded OTAFIX-2.4.6-bootloader-mota.zip before running the command above. The same CI job runs python3 -B -m unittest discover -s tools/lora_ota -p test_lora_ota_bootloader_version.py -v: simulated old-firmware replies and lost optional probes must not block either OTA launcher, while required capability, identity, storage, codec and package checks must still reject unsafe updates.

A green [PASSED] per suite means GoogleTest returned 0 (all assertions passed). PlatformIO's "0 test cases" line is just its Unity-style counter and does not reflect the GoogleTest count -- run the built binary directly (.pio/build/native/program) to see the per-assertion breakdown.

Suites

Suite	Source under test	Covers
`test_mqtt_presets`	`src/helpers/MQTTPresets.h`	preset lookup; table integrity (unique names, non-empty URLs, JWT-audience invariant, names fit the slot buffer); `mqttPresetNeedsSlotCredentials`; slot-count constants
`test_observer_validation`	`src/helpers/MQTTObserverValidation.h`	IATA (exactly 3 alphanumerics), owner key (64 hex), NTP hostname, and the buffer-fit check behind the #17 length validation -- including boundaries and nulls
`test_webconfig_keys`	`src/helpers/WebConfigKeys.h`	POST-key allowlist and reboot classification, secret detection, admin-password and browser-terminal command validation, slot-index bounds, and short-input guards
`test_webconfig_batch`	`src/helpers/WebConfigBatch.h`	config POST/replay/busy decisions; paced command drain; setup WiFi validation/IP handoff, including channel-change suppression; reboot confirmation/fallback; stop/refcount gating; exact timing and rollover boundaries
`test_topic_template`	`src/helpers/MQTTTopicTemplate.h`	`{iata}/{device}/{token}/{type}` expansion, overflow/NUL-termination, and a buffer-size fuzz
`test_mqtt_topic_router`	`src/helpers/MQTTTopicRouter.h`	complete preset/custom topic-routing contract; MeshRank all types except raw; required identifiers; invalid inputs/slots; exact buffer boundaries
`test_mqtt_connection_policy`	`src/helpers/MQTTConnectionPolicy.h`	reconnect guard/backoff/stagger and breaker transitions; stable reset; JWT lifetime/renewal policy; exact timing boundaries and 32-bit `millis()` rollover
`test_wifi_reconnect_policy`	`src/helpers/WiFiReconnectPolicy.h`	five-minute forced reconnect cadence, connection resets, duplicate disconnect observations, and 32-bit `millis()` rollover
`test_radio_liveness`	`src/helpers/RadioLivenessTracker.h`, `src/helpers/radiolib/RxBoostedGainDefaults.h`	staged radio recovery, activity reset and rollover handling; target-specific RX boosted-gain defaults and SX126x precedence
`test_lr1110_rx_recovery`	`src/helpers/radiolib/LR1110RxRecovery.h`	LR1110 four-byte RX-buffer shift signature; captured and accumulated shifts; ordinary/scoped packet exclusions
`test_mqtt_packet_queue_policy`	`src/helpers/MQTTPacketQueuePolicy.h`	queue-full eviction; stale-disconnect flush; adaptive drain limits; bounded QoS0 retries; exact timing boundaries and 32-bit `millis()` rollover
`test_mqtt_packet_filter`	`src/helpers/MQTTPacketFilter.h`	per-slot 0-15 allowlist parsing/formatting, numeric and named spellings; exact bounds; membership; candidate/eligible split and retry-completion policy; pre-queue union gate; default-mask detection
`test_mqtt_runtime_buffer_lifecycle`	`src/helpers/MQTTRuntimeBufferLifecycle.h`	idempotent allocation/release; partial-allocation degradation; retry of only missing buffers
`test_mqtt_prefs_codec`	`src/helpers/MQTTPrefsStorage.h`, `src/helpers/MQTTPrefsCodec.h`, `src/helpers/CompanionMqttPrefsNvs.h`	binary pre-slot/3-slot/6-slot and display-tail migration fixtures; v1 header integrity; fixed Companion rollback/recovery shapes; downgrade preservation; shortest-payload write policy
`test_mqtt_prefs_atomic_store`	`src/helpers/MQTTPrefsAtomicStore.h`	transactional MQTT writes and legacy `/node_prefs` handoff; exact short-write detection; begin/finish/rename failure cleanup; original-file preservation
`test_mqtt_prefs_json_import`	`src/helpers/MQTTPrefsJsonImport.h`, `src/helpers/MQTTPrefsSerializer.h`	one-time observer `/mqtt.json` v1 import grammar, strict schema/repair rules, binary-first precedence, future/artifact preservation, display-tail encoding, and atomic commit failure routing
`test_display_viewport`	`src/helpers/ui/DisplayViewport.h`, `src/helpers/ui/DisplayFrameSignature.h`	portrait logical-to-physical mapping, span coverage, fitted-width conversion, text scaling, and visible-frame signatures
`test_display_driver`	`src/helpers/ui/DisplayDriver.h`, `DisplayTextLayout.h`, `CompanionHomeLayout.h`	UTF-8-safe ellipsis/wrapping; maximum SSID and long setup-address bounds; Indicator 320/native-480 home info/pairing separation and enlarged-text placement; compact 128x64 pairing replacement; stale-region clearing
`test_indicator_font_stage_v2_protocol`	`src/helpers/IndicatorFontStageV2Protocol.h`	fail-closed STAGEV2 negotiation and legacy fallback; exact cumulative ACK parsing; 512-byte block boundaries, short final blocks, and real font-asset transfer geometry
`test_radio_activity_window`	`src/helpers/RadioActivityWindow.h`	rolling minute buckets, derived rates, expiry, warm-up, silence, saturation, and `millis()` rollover
`test_observer_dashboard`	`src/helpers/ui/ObserverDashboard.h`	landscape and portrait dashboard layout bounds, compact formatting, graph scaling, row signatures, and partial repaint policy
`test_touch_tap_detector`	`src/helpers/ui/TouchTapDetector.h`	debounced one-shot taps, bounce and long-press handling, minimum gaps, reset, and `millis()` rollover
`test_prefs_save_routing`	`src/helpers/PrefsSaveRouting.h`	runtime common/observer setters write only their owning preference image; mixed-owner setters and migrations can deliberately write both
`test_mqtt_payload_builder`	`src/helpers/MQTTPayloadBuilder.cpp`	status/packet/raw JSON contracts; optional fields; escaping; RX metrics and path; score handling; exact buffer bounds; maximum representative payloads
`test_telemetry_history`	`src/helpers/TelemetryHistory.h`, `ExternalVoltageHistory.h`	30-minute rings; seven-day temperature/battery and four-day multi-channel I2C voltage retention; exact 1 C temperature/status and 0.02 V packed voltage encodings; zero-only channel omission; Base64 pages and raw chunks; GPS differentials, resize preservation, heap budgets, and paging bounds
`test_flood_filter_policy`	`src/helpers/FloodFilterPolicy.h`	unordered blacklist matching; ordered 1/2/3-byte pbyte rule prefixes; original incoming scope classes and canonical region-name identity; channel-authentication cache key comparison; priority ordering and terminal stop masks; bridge-bucket and regionless channel-target selector encoding; `require=region` and per-channel scope-gate truth tables; fast/slow timing; adding, replacing, and preserving packet scope
`test_logical_message_cache`	`src/helpers/LogicalMessageCache.h`	bounded logical-message mapping; stable retry timestamps; exact older retries after newer messages; stale and same-timestamp mismatch rejection
`test_cli_command_utils`	`src/helpers/CLICommandUtils.h`, `src/helpers/ContactListOrder.h`, `src/helpers/TerminalCommandTracker.h`, `src/helpers/TerminalDisplayFilter.h`, `src/helpers/WiFiChannelPolicy.h`, `src/helpers/bridges/ESPNowBridgeFormat.h`	terminal verb/argument/path parsing; routed receive labels; quiet display defaults and independent emergency filtering; favorite-first contact ordering; standalone WiFi validation including 64-hex WPA/WPA2 PSKs; strict ESP-NOW channel and bridge-format parsing/range/fallback; single-command reply matching, round-trip timing, and rollover-safe expiration
`test_espnow_raw_fragmentation`	`src/helpers/ESPNowRawFragmentation.h`	byte-exact legacy raw frames; 251-255-byte two-frame encoding; CRC-32 integrity; source-MAC-keyed bounded reassembly; malformed, duplicate, out-of-order, timeout, rollover, and capacity handling
`test_gps_time_validation`	`src/helpers/sensors/GpsTimeValidation.h`	complete NMEA UTC validation; leap years and calendar bounds; rejection of receiver-default and signed-32-bit-out-of-range dates
`test_i2c_address_claim_policy`	`src/helpers/sensors/I2CAddressClaimPolicy.h`, `src/helpers/sensors/NmeaSentenceProbe.h`	a positively identified I2C GPS owns only its address on its bus; an INA3221 identity match blocks conflicting u-blox writes; UART GPS detection requires a complete checksum-valid GPS NMEA sentence
`test_gps_transport_ownership`	`src/helpers/SensorManager.cpp`	temporary bridge ownership cancels GPS acquisition/holds, preserves user preference/cache, and restores GPS only after the UART is released
`test_identity_generation`	`src/helpers/IdentityGeneration.h`	reserved-prefix rejection; bounded retries; final provisioned attempt; fail-closed exhaustion
`test_remote_cli_reply_cache`	`src/helpers/RemoteCliReplyCache.h`, `src/helpers/RemoteCliRequest.h`, `src/helpers/RemoteCliTimeout.h`	authenticated logical-request matching; bounded recent-reply history; backward-compatible retry identity; 300% response timeout; empty-response completion; on-air truncation and clearing
`test_companion_frame_queue`	`src/helpers/CompanionFrameQueue.h`, `src/helpers/CompanionHardwareCommandCompat.h`	response/required/best-effort classification; reserved capacity; stable priority; safe eviction; message-waiting coalescing; command `0x42` framed-CLI disambiguation and deprecated hardware-alias mapping
`test_companion_status_response`	`src/helpers/CompanionStatusResponse.h`	request-tag correlation and minimum status-response length, including rejection of the three-entry ACL payload that previously masqueraded as status
`test_companion_terminal_diagnostics`	`src/helpers/CompanionTerminalDiagnostics.h`	bounded Full Companion ESP32 heap/PSRAM/offline-queue diagnostic formatting, including truthful no-PSRAM output
`test_serial_mode_switch`	`src/helpers/ArduinoSerialInterface.cpp`, `src/helpers/MultiSerialInterface.h`	terminal/seeder control-sequence recognition, single-TTY logging transitions, and USB/TCP ownership; queued/atomic USB output under backpressure and short writes; partial-frame busy state; requester-affine replies, locked contact streams, and Bluetooth-only pairing routing
`test_ble_tx_stall_watchdog`	`src/helpers/BleTxStallWatchdog.h`	exact BLE fragment progress; blocked-reply timeout; rollover-safe elapsed time; disconnect recovery retry and completion
`test_ble_mota_control`	`src/helpers/BleMotaStream.h`, `CompanionMotaControl.h`	encrypted mOTA channel ring buffering, overflow fail-closed behavior, request gating, and strict rejection of injected or USB-ownership control commands
`test_atomic_file_writer`	`src/helpers/AtomicFileWriter.h`	verified temporary-file commit; short-write, readback, validation, and rename failures; preservation of the live file and stale-temp cleanup
`test_client_login_persistence`	`src/helpers/ClientLoginPersistence.h`, `LazyPersistence.h`	pre-allocation durable replay reservations; reboot, ACL-eviction, and revoked-admin tombstones; bounded-store policy (low-trust no-insert, privileged fail-closed); atomic replay-file recovery, including post-commit cleanup failure; preauthorized transient refresh; admin/guest promotion and downgrade; force-flood preservation; role masking and fixed-size secret copy
`test_client_path_persistence`	`src/helpers/ClientPathPersistence.h`, `LazyPersistence.h`	encoded path identity and byte lengths; unknown, zero-hop, force-flood, and nonpersistent clients; replay-unqualified RAM-only routes preserve an earlier operator route across unrelated save/reload
`test_temp_radio_reply_barrier`	`src/helpers/TempRadioReplyBarrier.h`, `TempRadioLeaseDeadline.h`	exact single-copy queued reply completion/failure handoff; suppression of untracked alternate/retry copies; rejection of foreign callbacks; cancellation; monotonic hard expiry that a backward wall-clock correction cannot extend; bounded remaining-time reporting
`test_lazy_persistence`	`src/helpers/LazyPersistence.h`	first-write scheduling without postponement, zero-sentinel rollover preservation, capped exponential save-failure backoff that mutations cannot defeat, and reset only after success
`test_client_acl_file_transaction`	`src/helpers/ClientACLFileTransaction.h`	verified temp publication, preservation of the prior ACL on verification/rename failure, post-commit cleanup-failure handling, and recovery at every temp/backup/primary boundary
`test_cad_timing`	`src/helpers/radiolib/CadTiming.h`, `LR2021SideDetectorConfig.h`, `RadioAirtime.h`	Cascade and slow-profile CAD deadlines; invalid airtime handling; bounded LR2021 side-detector parsing and LDRO recomputation
`test_companion_node_prefs`	`examples/companion_radio/NodePrefs.h`	independent device power saving, RXPS, Wi-Fi, FEM, Bluetooth name, address policy and stealth flag; random-static address validation/generation; idempotent stealth toggles, pairing reset and armed rotation policy matching; one-time migration of the regressed power-saving default
`test_config_serializer`	`src/helpers/ConfigSerializer.cpp`, Companion `NodePrefs`	escaped config save/load, whitespace and malformed input, unknown fields, and FEM/ESP-NOW bridge-format preference round trips
`test_deferred_cli_command`	`src/helpers/DeferredCliCommand.h`	copying authenticated command context, single-pending-command enforcement, clearing, and length rejection
`test_host_cli_bridge`	`src/helpers/HostCliBridge.h`	bounded request/reply parsing, Base64URL serial framing, correlation preservation, one-time service-claim proofs, request-token fields, line safety, and UTF-8-safe truncation
`test_kiss_modem`	`examples/kiss_modem/KissModem.cpp`	KISS escaping/framing and packet metadata under partial writes, host TX backpressure, queue saturation, and radio completion; run with `native_kiss_modem`
`test_mesh_tables`	`src/helpers/SimpleMeshTables.h`	packet and ACK/multipart deduplication, scope-independent identity, route-prefix matching, and deterministic recent-repeater expiry/eviction
`test_mqtt_lifecycle`	`src/helpers/MQTTLifecycle.h`	idempotent start/stop, initialization rollback, cooperative stop acknowledgment and timeout, callback ownership, restart, and the OTA flash barrier
`test_mqtt_reply_format`	`src/helpers/MQTTReplyFormat.h`	bounded formatted appends, exact-fit and one-byte buffers, truncation, NUL termination, and invalid starting positions
`test_packet_manager`	`src/Packet.cpp`, `src/Dispatcher.cpp`, `src/helpers/StaticPoolPacketManager.cpp`	truncated-packet rejection, unavailable-radio behavior, scoped RX-delay replacement, queue/CAD scheduling, and staged radio/TX recovery
`test_persistent_store_format`	`src/helpers/PersistentStoreFormat.h`	contact-page headers and CRCs, dirty-page state, stable slot allocation, and bounded resumable legacy migration across power loss
`test_power_management`	`src/helpers/PowerManagementUtils.h`	median filtering of a brownout outlier and valid-reading requirements for the boot lock
`test_rx_power_saving`	`src/helpers/radiolib/RXPowerSaving.h`	guarded timer/capture bounds across SF5-SF12, bandwidths, TCXO delays and wire preambles; experimental profiles; retuning and strict CLI parsing
`test_noise_floor_estimator`	`src/helpers/radiolib/NoiseFloorEstimator.h`	spaced low percentile, captured off-SF traffic, weighting, contamination limits, persistent rises, resets and clock rollover
`test_region_names`	`src/helpers/RegionNameUtils.h`	canonical public-region markers while preserving distinct private and differently named regions
`test_datagram_payload_limits`	`src/helpers/DatagramPayloadLimits.h`	encrypted datagram plaintext ceilings, including the anonymous region-reply prefix and worst-case cipher padding
`test_serial_packet_log`	`src/helpers/SerialPacketLog.h`	bounded USB packet logging and dropped-line reporting
`test_alert_fault_policy`	`src/helpers/AlertFaultPolicy.h`	coherent WiFi/MQTT outage edges, durations, rate limits, and formatting
`test_routing_policy`	`src/helpers/RoutingPolicy.h`	scoped/unscoped flood hop limits and selection of direct, path-return, mirrored-scope, default-scope, or unscoped replies
`test_rs232_uart`	`src/helpers/bridges/RS232UartUtils.h`	stopping the active UART peripheral before reassigning its pins
`test_security_session_timer`	`src/helpers/nrf52/SecuritySessionTimer.h`	two-minute security-session expiry, cancellation, restart, and `millis()` rollover
`test_trace_path_helpers`	`src/helpers/TracePathHelpers.h`	round-trip route construction, hash-width conversion, raw path parsing/limits, and terminal trace timeout bounds
`test_user_gpio`	`src/helpers/UserGpio.cpp`, `UserGpioReplyTracker.h`	board-approved pins, get/set/reset, timed nonblocking transitions, duplicate suppression, rollover, and completion-reply routing
`test_utf8_helpers`	`src/helpers/UTF8Helpers.h`	byte-limit truncation at complete code-point boundaries and rejection of malformed or truncated UTF-8
`test_wifi_ota_seeder_policy`	`src/helpers/WiFiOtaSeederPolicy.h`, `WiFiOtaSeederStatus.h`	listener state versus network availability, serial/TCP folder ownership, detach detection, and bounded status formatting
`test_tls_clock_validity`	`src/helpers/esp32/TlsClockValidity.h`	signed wall-clock minimum and the fresh-proof/WiFi/time conjunction required before certificate-validating downloads
`test_ota`	`src/helpers/ota/`	v2 application/v3 bootloader parser separation; legacy XIAO, generic internal, and exact MeshTower V2 SD embedded identity, vector, capability, explicit-confirmation, codec-isolation, scratch-headroom/shared-slot no-EndF gates, and no-autofetch gates; container and EndF integrity; protocol codecs; transfer, resume, and layered apply safety; adaptive 2-to-4 block-request window growth and stall contraction; active-transfer priority classification
`test_flood_advert_limiter`	`FloodAdvertLimiter.h/.cpp`, `FloodAdvertCLI.h`	hop-based quotas, verified duplicates, prefix collisions, abuse escalation/recovery, protected capacity, rollover, exact-key clearing, read-only listing, pagination, malformed selectors, full-key details, and USB/LoRa reply bounds
`test_trace_retry`	`src/Mesh.cpp`, `RTCClock`, `ClockSyncUtils.h`, retry and relay policy	app-v2 and boot-v3 traffic sharing `PAYLOAD_TYPE_OTA=0x0C` and the TempRadio suspend policy; opaque OTA relay behavior; background discovery priority; immediate primary transfer relay, receive-delay bypass, fast CAD retry, and no generic flood retry; trace and non-OTA flood retry timing; backward RTC correction; clock consensus/path policy and the 10-minute default drift threshold; advert receive/forward limits and matching read-only CLI listings
`test_utils`	`src/Utils.cpp`	`Utils::toHex` (upstream)

Conventions (and how to add a suite)

Each test/test_<name>/ directory builds into its own GoogleTest program and must define its own main() (::testing::InitGoogleTest + RUN_ALL_TESTS).
Tests are host-only: include only pure headers. Arduino/crypto stubs live in test/mocks/ (on the include path via -I test/mocks).
Firmware headers are included from src (via -I src, e.g. #include "helpers/MQTTPresets.h"). Some are guarded or ESP-flavored, so a suite may need shims before the include -- e.g. test_mqtt_presets does #define WITH_MQTT_BRIDGE 1 (the preset table is behind that flag) and #define PROGMEM (the embedded CA-cert strings are PROGMEM-qualified).
To add a suite: create test/test_<name>/test_<name>.cpp with a main(), and add any host-only source it links to the native env's build_src_filter in platformio.ini (header-only code needs no source entry). No other wiring.
Keep logic testable by extracting pure functions into headers (as MQTTObserverValidation.h / WebConfigKeys.h / MQTTTopicTemplate.h do) and having the firmware call the same functions.