Why VScode PlatformIO unit test can not use function declare in header file?

VScode PlatformIO unit test can not use function declare in header file, but use the function definition code is work. It show undefined reference to `wifiInit()' Code

#include <unity.h>

#include "wifi/wifi.h"

void test_unit() {
    TEST_ASSERT_EQUAL(EXIT_SUCCESS,wifiInit());
}

void setup() {
    delay(2000);
    UNITY_BEGIN(); 
    RUN_TEST(test_unit);
}

void loop() {}

#include <Arduino.h>
#include <WiFi.h>

#ifndef __wifi_init_h_
#define __wifi_init_h_

#define WIFI_SSID "**"
#define WIFI_PASSWD "***"

int wifiInit();
#endif

#include "wifi/wifi.h"

int wifiInit() {
    // 设置ESP32通过WIFI连接网络
    WiFi.begin(WIFI_SSID, WIFI_PASSWD);
    WiFi.config(WiFi.localIP(), WiFi.gatewayIP(), WiFi.subnetMask(), (uint32_t)0xDF050505, (uint32_t)0x72727272);
    // 打印连接状态
    Serial.println("Connecting");
    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.print(".");
    }
    Serial.print("\nIP address: ");
    Serial.println(WiFi.localIP());
    return EXIT_SUCCESS;
}
}

I coyied the wifiInit() in wifi.cpp to the wifi.h, it worked.