feat(doc): Add node & test documentation

doc/tests/WheelDataSimulator.md

@@ -0,0 +1,73 @@
+# Wheel Data Simulator Unit Tests
+
+Unit tests for the `DataSimulator` (Wheel) node are implemented in `src/g2_2025_odometry_pkg/test/test_wheel_simulator.cpp` using Google Test and ROS2 test utilities. The tests validate node initialization, message publishing, array structure, and data correctness.
+
+## Test Cases
+
+### 1. NodeInitialization
+
+**Description:** Verifies that the Wheel DataSimulator node can be created without errors.
+
+- **Test Action:** Create DataSimulator instance
+- **Expected Result:** No exceptions thrown during construction
+
+### 2. WheelDataPublishing
+
+**Description:** Tests that wheel data messages are published on the correct topic.
+
+- **Test Action:**
+  - Create subscription to `simulated_wheel_data` topic
+  - Create DataSimulator node
+  - Spin both nodes for a short period
+- **Expected Result:** At least one `std_msgs/msg/Float64MultiArray` message is received
+
+### 3. WheelDataArraySize
+
+**Description:** Verifies that the published array contains the correct number of wheel values.
+
+- **Test Action:**
+  - Subscribe to `simulated_wheel_data`
+  - Receive a message
+  - Check array size
+- **Expected Result:** `data.size()` equals 4 (FL, FR, RL, RR)
+
+### 4. ValidVelocityValues
+
+**Description:** Tests that all wheel velocity values are valid (finite numbers).
+
+- **Test Action:**
+  - Subscribe and receive wheel data message
+  - Check each value in the array
+- **Expected Result:** All 4 values are finite numbers
+
+### 5. MultipleMessagesReceived
+
+**Description:** Tests that multiple messages are published over time.
+
+- **Test Action:**
+  - Subscribe and count received messages
+  - Spin for a short duration
+- **Expected Result:** Message count is greater than 0
+
+## Test Infrastructure
+
+The test class `WheelSimulatorTest` provides:
+- Static `SetUpTestSuite()` and `TearDownTestSuite()` for ROS2 init/shutdown
+- Helper method `setupBasicWheelParams()` for setting up default test parameters
+
+## ROS2 Topics Used
+
+| Topic | Message Type | Direction |
+|-------|--------------|-----------|
+| `simulated_wheel_data` | std_msgs/msg/Float64MultiArray | Published by node under test |
+
+## Data Array Format
+
+The published Float64MultiArray contains wheel values in the following order:
+
+| Index | Wheel |
+|-------|-------|
+| 0 | Front Left (FL) |
+| 1 | Front Right (FR) |
+| 2 | Rear Left (RL) |
+| 3 | Rear Right (RR) |