Added TokenService unit tests

src/test/java/ntnu/idatt2016/v233/SmartMat/service/TokenServiceTest.java

+package ntnu.idatt2016.v233.SmartMat.service;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.authority.SimpleGrantedAuthority;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.jwt.JwtEncoder;
+import org.springframework.security.oauth2.jwt.JwtEncoderParameters;
+
+import java.time.Instant;
+import java.util.Arrays;
+import java.util.Collection;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class TokenServiceTest {
+
+    private TokenService tokenService;
+    private JwtEncoder jwtEncoder;
+
+    @BeforeEach
+    void setUp() {
+        jwtEncoder = mock(JwtEncoder.class);
+        tokenService = new TokenService(jwtEncoder);
+    }
+
+    @Test
+    void testGenerateToken() {
+        // Given
+        Collection<SimpleGrantedAuthority> authorities = Arrays.asList(
+                new SimpleGrantedAuthority("ROLE_ADMIN"),
+                new SimpleGrantedAuthority("ROLE_USER")
+        );
+        Authentication authentication = new UsernamePasswordAuthenticationToken("user", "password", authorities);
+
+        Instant now = Instant.now();
+        Jwt jwt = Jwt.withTokenValue("test-token")
+                .header("alg", "none")
+                .claim("iss", "self")
+                .claim("issuedAt", now)
+                .claim("expiresAt", now)
+                .claim("sub", "user")
+                .claim("scope", "ROLE_ADMIN ROLE_USER")
+                .build();
+
+        when(jwtEncoder.encode(any(JwtEncoderParameters.class))).thenReturn(jwt);
+
+        // When
+        String token = tokenService.generateToken(authentication);
+
+        // Then
+        assertNotNull(token);
+        assertEquals("test-token", token);
+    }
+}