feat: implement MailModule with email services and tests

Added MailModule with services for email validation and password reset functionalities. Includes configuration via `@nestjs-modules/mailer` and comprehensive unit tests.

backend/src/mail/mail.service.spec.ts

@@ -0,0 +1,87 @@
+import { Logger } from "@nestjs/common";
+import { ConfigService } from "@nestjs/config";
+import { Test, TestingModule } from "@nestjs/testing";
+import { MailerService } from "@nestjs-modules/mailer";
+import { MailService } from "./mail.service";
+
+describe("MailService", () => {
+	let service: MailService;
+	let mailerService: MailerService;
+
+	beforeEach(async () => {
+		const module: TestingModule = await Test.createTestingModule({
+			providers: [
+				MailService,
+				{
+					provide: MailerService,
+					useValue: {
+						sendMail: jest.fn().mockResolvedValue({}),
+					},
+				},
+				{
+					provide: ConfigService,
+					useValue: {
+						get: jest.fn().mockReturnValue("test.io"),
+					},
+				},
+			],
+		}).compile();
+
+		service = module.get<MailService>(MailService);
+		mailerService = module.get<MailerService>(MailerService);
+	});
+
+	it("should be defined", () => {
+		expect(service).toBeDefined();
+	});
+
+	it("should send validation email with correct URL", async () => {
+		const email = "test@example.com";
+		const token = "token123";
+		await service.sendEmailValidation(email, token);
+
+		expect(mailerService.sendMail).toHaveBeenCalledWith(
+			expect.objectContaining({
+				to: email,
+				subject: "Validation de votre adresse email",
+				html: expect.stringContaining(
+					"https://test.io/api/auth/verify-email?token=token123",
+				),
+			}),
+		);
+	});
+
+	it("should send password reset email with correct URL", async () => {
+		const email = "test@example.com";
+		const token = "token123";
+		await service.sendPasswordReset(email, token);
+
+		expect(mailerService.sendMail).toHaveBeenCalledWith(
+			expect.objectContaining({
+				to: email,
+				subject: "Réinitialisation de votre mot de passe",
+				html: expect.stringContaining(
+					"https://test.io/api/auth/reset-password?token=token123",
+				),
+			}),
+		);
+	});
+
+	it("should throw and log error when sending fails", async () => {
+		const email = "test@example.com";
+		const token = "token123";
+		const error = new Error("SMTP Error");
+		(mailerService.sendMail as jest.Mock).mockRejectedValueOnce(error);
+
+		const loggerSpy = jest
+			.spyOn(Logger.prototype, "error")
+			.mockImplementation(() => {});
+
+		await expect(service.sendEmailValidation(email, token)).rejects.toThrow(
+			"SMTP Error",
+		);
+
+		expect(loggerSpy).toHaveBeenCalled();
+		loggerSpy.mockRestore();
+	});
+});