Finish unit testing code for esp32 draft (#28)

_drafts/unit-testing-code-for-esp32.md → _drafts/2024-10-30-unit-testing-code-for-esp32.md

@@ -2,8 +2,8 @@
 title: Unit Testing Code for ESP32
 author: adrian.ancona
 layout: post
-# date: 2024-10-23
-# permalink: /2024/10/unit-testing-code-for-esp32/
+date: 2024-10-30
+permalink: /2024/10/unit-testing-code-for-esp32/
 tags:
   - esp32
   - programming
@@ -18,7 +18,7 @@ There are a few ways we can go about unit testing code written for ESP32:
 - Run tests using an emulator
 - Run tests on Linux host using mocks
 
-In this article we are going to learn how to write tests that can run on a Linux host, so it's easy to plug them to a CI system.
+We are going to learn how to write tests that can run on a Linux host, so it's easy to plug them to a CI system.
 
 <!--more-->
 
@@ -39,7 +39,7 @@ library-root/
     └── ...
 ```
 
-We are going to use the [Catch2](https://github.com/catchorg/Catch2) to run our unit tests because we just need to download a single file from Github. Copy the contents of [catch.hpp](https://github.com/catchorg/Catch2/blob/v2.x/single_include/catch2/catch.hpp) into `library-root/test/external/catch2/catch.hpp`.
+We are going to use [Catch2](https://github.com/catchorg/Catch2) to run our unit tests because we just need to download a single file from Github. Copy the contents of [catch.hpp](https://github.com/catchorg/Catch2/blob/v2.x/single_include/catch2/catch.hpp) into `library-root/test/external/catch2/catch.hpp`.
 
 We can create `library-root/test/CMakeLists.txt` to run our tests:
 
@@ -143,7 +143,7 @@ TEST_CASE("parseQueryString") {
 }
 ```
 
-If we run compile and run our tests now, we will get an error, because we haven't defined `parse_query_string`:
+If we compile and run our tests now, we will get an error, because we haven't defined `parse_query_string`:
 
 ```
 /library-root/test/src/test-main.cpp: In function 'void C_A_T_C_H_T_E_S_T_0()':
@@ -212,8 +212,119 @@ parse_query_string(const std::string &line) {
 }
 ```
 
-At this point our library doesn't use any esp-idf specific functionality, but it can be used by esp-idf projects and we can write tests for it.
+At this point, our library doesn't use any esp-idf specific functionality, but it can be used by esp-idf projects, and we already wrote a test for it.
 
 ## Mocking esp-idf
 
+When our code depends on esp-idf, we will need to mock the functionality in order to test it.
 
+Let's say we have this code in `library-root/src/library.hpp`:
+
+```cpp
+#pragma once
+
+#include <esp_err.h>
+
+esp_err_t event_loop();
+```
+
+And this in `library-root/src/library.cpp`:
+
+```cpp
+#include "library.hpp"
+
+#include <esp_event.h>
+
+esp_err_t event_loop() {
+  return esp_event_loop_create_default();
+}
+```
+
+We have introduced 2 ESP-IDF dependencies: `esp_err.h` and `esp_event.h`. To be able to write tests for this code, we will need to mock those dependencies.
+
+We'll start by creating `library-root/test/mock/` folder. This will be the place where we'll add our mocks. We have the freedom to make our mocks do whatever we desire.
+
+For this example, we'll keep them very simple.
+
+library-root/test/mock/esp_err.h:
+
+```cpp
+#pragma once
+
+#define ESP_OK 0
+
+typedef int esp_err_t;
+```
+
+library-root/test/mock/esp_event.h:
+
+```cpp
+#pragma once
+
+#include "esp_err.h"
+
+esp_err_t esp_event_loop_create_default();
+```
+
+library-root/test/mock/esp_event.cpp:
+
+```cpp
+#include "esp_event.h"
+
+esp_err_t esp_event_loop_create_default() {
+  return ESP_OK;
+}
+```
+
+We also need to update `library-root/test/CMakeLists.txt`, so it knows where to find the mocks:
+
+```cpp
+cmake_minimum_required(VERSION 3.27.4)
+project(LibraryTest
+  VERSION 0.1.0
+  LANGUAGES CXX)
+
+include_directories(external/catch2)
+include_directories(../include)
+include_directories(mock)
+
+FILE(GLOB MOCK_SRCS mock/*.cpp)
+
+set(TESTING_SRCS
+  ../src/library.cpp
+)
+
+set(TEST_TARGET_SRCS
+  src/test-main.cpp
+)
+
+add_compile_options(-Wall -Wextra -Wpedantic -Werror)
+
+add_executable(
+  test
+  ${MOCK_SRCS}
+  ${TEST_TARGET_SRCS}
+  ${TESTING_SRCS}
+)
+```
+
+Now, we can write a test:
+
+```cpp
+#define CATCH_CONFIG_MAIN
+#include <catch.hpp>
+
+#include "library.hpp"
+
+TEST_CASE("event_loop") {
+  SECTION("Returns ESP_OK") {
+    REQUIRE(event_loop() == ESP_OK);
+  }
+}
+```
+
+## Conclusion
+
+Writing tests for ESP-IDF is not very complicated once we know what to do. The biggest hurdle is probably writing the tests, which, depending on the amount of dependencies, might be a lot of work.
+
+As usual, you can find a working example in [my examples' repo](https://github.com/soonick/ncona-code-samples/tree/master/unit-testing-code-for-esp32).