test: Add Readme to api-test app (#48)

Author: damcav64

README.md

@@ -1,2 +1,8 @@
 # firebolt-cpp-client
 Implementation of Firebolt C++ Client.
+
+## API Test App
+
+For usage instructions of the API test application, see:
+
+- [test/api_test_app/README.md](test/api_test_app/README.md)

test/api_test_app/README.md

@@ -0,0 +1,123 @@
+# API Test App
+
+`api-test-app` is a CLI demo/test utility for exercising Firebolt C++ client APIs.
+It can connect to a local mock service, a platform service, or any endpoint set through an environment variable.
+It can be run in either interactive or auto mode.
+In interactive mode, the user can select which APIs to call via a menu system.
+In auto mode, every API method is called sequentially, with no input from the user.
+
+All output is to stdout.
+
+## Executable Name
+
+The app binary name is:
+
+`api-test-app`
+
+## Command Line Usage
+
+```bash
+api-test-app [--auto] [--mock] [--platform] [--dbg] [--help]
+```
+
+### Options
+
+- `--auto`  
+ Run all methods for all interfaces automatically.
+
+- `--mock`  
+ Use local mock endpoint: `ws://127.0.0.1:9998/`.
+
+- `--platform`  
+ Use platform endpoint: `ws://127.0.0.1:3474/`.
+
+- `--dbg`  
+ Enable debug logging.
+
+- `--help`  
+ Print usage and exit.
+
+## Endpoint Selection Priority
+
+The app chooses the WebSocket endpoint in this order:
+
+1. `--mock` or `--platform` (if provided)
+2. `FIREBOLT_ENDPOINT` environment variable (if set)
+3. Default fallback: `ws://127.0.0.1:9998/`
+
+At startup, the app prints the selected URL:
+
+```text
+Using firebolt URL: <url>
+```
+
+## Run Modes
+
+### 1) Interactive mode (default when stdin is a TTY)
+
+- Shows a menu of interfaces.
+- After selecting an interface, shows its methods.
+- Runs selected methods on demand.
+
+### 2) Auto mode (`--auto`)
+
+- Runs every method of every interface sequentially.
+- Prints each interface and method before execution.
+
+### 3) Piped stdin mode (non-TTY stdin)
+
+When input is piped in, the app automatically switches to autorun behavior for command processing and reads one method name per line.
+
+Each line must match a method string exactly (for example, `Accessibility.highContrastUI`).
+If a method is unknown, it prints:
+
+```text
+Method not found: <input>
+```
+
+## Examples
+
+### Use mock service (default behavior in helper script)
+
+```bash
+api-test-app --mock
+```
+
+### Connect to platform service with debug logs
+
+```bash
+api-test-app --platform --dbg
+```
+
+### Use custom endpoint via environment
+
+```bash
+export FIREBOLT_ENDPOINT="ws://192.168.1.50:3474/"
+api-test-app
+```
+
+### Run all methods automatically
+
+```bash
+api-test-app --auto --mock
+```
+
+### Run methods from a test suite file
+
+```bash
+cat test-suite.example | api-test-app --mock
+```
+
+## Connection Behavior
+
+- The app attempts to connect and waits up to 2 seconds for initial connection.
+- It exits with non-zero status if connection setup fails or times out.
+- On completion, it disconnects cleanly.
+
+## Build Script Notes
+
+The local helper script `build.sh` in this directory:
+
+- Builds the app in `build/`
+- Runs `build/api-test-app --mock` by default
+- Supports options such as `--clean`, `--no-run`, `--just-run`, and `--sysroot`