Add QUICK_TEST mode documentation to testing.md

Author: dnotestein

doc/devs/testing.md

@@ -30,3 +30,64 @@ genhtml interesting.info --output-directory lcov --prefix `pwd`
 ```
 
 Now open `lcov/index.html` in a browser
+
+# CI Testing
+
+## Quick Test Mode
+
+Quick Test mode allows running CI tests using pre-built binaries from a previous successful pipeline, skipping the ~20 minute C++ build step. This is useful when:
+
+- You're only changing test code, not hived source
+- You want fast feedback on test changes
+- You're debugging flaky tests
+
+### Usage
+
+Run a pipeline with these variables:
+
+| Variable | Required | Description |
+|----------|----------|-------------|
+| `QUICK_TEST` | Yes | Set to `true` to enable |
+| `QUICK_TEST_BINARY_COMMIT` | No | Specific commit SHA to use (auto-detects if empty) |
+| `QUICK_TEST_JOBS` | No | Additional test jobs to run (comma-separated) |
+| `QUICK_TEST_BLOCK_LOG_IMAGE` | No | Block log image for test_tools_tests |
+
+**Example - Basic quick test:**
+```bash
+glab ci run -b my-branch --variables QUICK_TEST:true
+```
+
+**Example - With specific binary commit:**
+```bash
+glab ci run -b my-branch --variables QUICK_TEST:true --variables QUICK_TEST_BINARY_COMMIT:abc1234f
+```
+
+**Example - Including test_tools_tests:**
+```bash
+glab ci run -b my-branch \
+  --variables QUICK_TEST:true \
+  --variables QUICK_TEST_JOBS:test_tools_tests \
+  --variables QUICK_TEST_BLOCK_LOG_IMAGE:registry.gitlab.syncad.com/hive/hive/block-log-5m:latest
+```
+
+### What Runs
+
+| Mode | Build Jobs | Test Jobs | Time |
+|------|------------|-----------|------|
+| Normal | All (~20 min) | All 50+ jobs | ~60+ min |
+| Quick Test | None | Unit tests only | ~30 min |
+
+By default, Quick Test runs only unit tests (`chain_test`, `plugin_test`). Use `QUICK_TEST_JOBS` to add more.
+
+### Finding Available Binaries
+
+To list recent testnet images available for Quick Test:
+```bash
+./scripts/ci-helpers/list-hive-binaries.sh
+```
+
+### Limitations
+
+- Binaries must exist in the registry from a previous successful pipeline
+- If your changes affect hived behavior, results may not reflect current code
+- Auto-detection uses the most recent testnet image tag