Created Documentation for unit tests: This based off the CTS in house…

… unit test framework

docs/C_Unit_Tests.md

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+# C Unit Tests
+
+This repo uses an in-house unit test framework, which is about as minimal as unit tests can be.
+
+## How to Write a Test
+
+The following guide demonstrates an example of creating a testable function, and then writing
+unit tests for that function.
+
+1.  Come up with a testable function (called the Function-Under-Test, or FUT). For examples:
+
+    ```c
+    // File: transforms/byte_transforms.c
+
+    #include "transforms/byte_transforms.h"
+
+    uint32_t GEN_convert_big_endian_four_byte_array_to_uint32(uint8_t four_byte_array[]) {
+        // recall: big endian means the Most Significant Bit (MSB) is at index 0 (left side)
+        return (four_byte_array[0] << 24) | (four_byte_array[1] << 16) |
+                (four_byte_array[2] << 8)  | four_byte_array[3];
+    }
+    ```
+
+2.  Create a new file in `Core/Src/unit_tests` called `test_bytes_transforms.c`. Create the unit test
+    function within that file:
+
+        ```c
+        // File: unit_tests/test_bytes_transforms.c
+
+        #include "unit_tests/unit_test_helpers.h" // for all unit tests
+        #include "transforms/byte_transforms.h" // for the Function-Under-Test
+
+        uint8_t TEST_EXEC__GEN_convert_big_endian_four_byte_array_to_uint32() {
+            // TODO: implement unit test later
+            TEST_ASSERT_TRUE(1 == 1);
+
+            return 0; // THIS LINE MUST BE INCLUDED to indicate the test passed
+        }
+        ```
+
+3.  Add the function prototype to the header file `Core/Inc/unit_tests/test_bytes_transforms.h`:
+
+    ```c
+    // File: unit_tests/test_bytes_transforms.h
+    // ...
+    uint8_t TEST_EXEC__GEN_convert_big_endian_four_byte_array_to_uint32();
+    // ...
+    ```
+
+4.  Add the test to the "inventory table" of tests in `Core/Src/unit_tests/unit_test_inventory.c`:
+
+    ```c
+    // File: unit_tests/unit_test_inventory.c
+    #include "unit_tests/test_byte_transforms.h"
+
+    const TEST_Definition_t TEST_definitions[] = {
+        // ...
+        // Add the following section:
+        {
+            .test_func = TEST_EXEC__GEN_convert_big_endian_four_byte_array_to_uint32,
+            .test_file = "transforms/byte_transforms",
+            .test_func_name = "GEN_convert_big_endian_four_byte_array_to_uint32"
+        },
+        // ...
+    };
+
+    ```
+
+5.  Flash the ESP32, and check the monitor ESP-IDF Monitor window. See that the test passes.
+
+6.  Go back to the `TEST_EXEC__GEN_convert_big_endian_four_byte_array_to_uint32` function, and implement
+    the test:
+
+        ```c
+        // File: unit_tests/test_bytes_transforms.c
+
+        uint8_t TEST_EXEC__GEN_convert_big_endian_four_byte_array_to_uint32() {
+            uint8_t test_array_1[4] = {0x12, 0x34, 0x56, 0x78};
+            uint32_t expected_result_1 = 0x12345678;
+            TEST_ASSERT_TRUE(GEN_convert_big_endian_four_byte_array_to_uint32(test_array_1) == expected_result_1);
+
+            uint8_t test_array_2[4] = {0xFE, 0xDC, 0xBA, 0x98};
+            uint32_t expected_result_2 = 4275878552; // 0xFEDCBA98
+            TEST_ASSERT_TRUE(GEN_convert_big_endian_four_byte_array_to_uint32(test_array_2) == expected_result_2);
+
+            return 0; // THIS LINE MUST BE INCLUDED to indicate the test passed
+        }
+        ```
+
+7.  Run the test again.