fix: update JwtService to handle default expiration and add tests for token generation

backend/src/test/kotlin/com/condado/newsletter/service/AuthServiceTest.kt

@@ -40,7 +40,7 @@ class AuthServiceTest {
     fun should_returnValidClaims_when_jwtTokenParsed() {
         val realJwtService = JwtService(
             secret = "test-secret-key-for-testing-only-must-be-at-least-32-characters",
-            expirationMs = 86400000L
+            expirationMsRaw = "86400000"
         )
         val token = realJwtService.generateToken()
 
@@ -51,7 +51,7 @@ class AuthServiceTest {
     fun should_returnFalse_when_expiredTokenValidated() {
         val realJwtService = JwtService(
             secret = "test-secret-key-for-testing-only-must-be-at-least-32-characters",
-            expirationMs = 1L
+            expirationMsRaw = "1"
         )
         val token = realJwtService.generateToken()
 

backend/src/test/kotlin/com/condado/newsletter/service/JwtServiceTest.kt

@@ -0,0 +1,26 @@
+package com.condado.newsletter.service
+
+import io.jsonwebtoken.Jwts
+import io.jsonwebtoken.security.Keys
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+
+class JwtServiceTest {
+
+    private val secret = "12345678901234567890123456789012"
+
+    @Test
+    fun should_generate_token_when_expiration_is_empty() {
+        val jwtService = JwtService(secret, "")
+
+        val token = jwtService.generateToken()
+
+        val claims = Jwts.parser()
+            .verifyWith(Keys.hmacShaKeyFor(secret.toByteArray(Charsets.UTF_8)))
+            .build()
+            .parseSignedClaims(token)
+            .payload
+
+        assertTrue(claims.expiration.after(claims.issuedAt))
+    }
+}