Add tests for auth dependencies and security utilities

Introduced unit tests for `get_current_user`, `get_current_active_user`, and security functions like token creation and decoding. Also refactored imports for consistency and cleaned up unused or misplaced code to improve maintainability.

backend/tests/auth/test_security.py

@@ -0,0 +1,68 @@
+import pytest
+from datetime import timedelta
+from jose import jwt, JWTError
+from app.auth.security import (
+    get_password_hash, verify_password,
+    create_access_token, create_refresh_token,
+    decode_token, SECRET_KEY, ALGORITHM
+)
+from app.schemas.token import TokenPayload
+
+
+def test_password_hashing():
+    plain_password = "securepassword123"
+    hashed_password = get_password_hash(plain_password)
+
+    # Ensure hashed passwords are not the same
+    assert hashed_password != plain_password
+    # Test password verification
+    assert verify_password(plain_password, hashed_password)
+    assert not verify_password("wrongpassword", hashed_password)
+
+
+def test_access_token_creation():
+    user_id = "123e4567-e89b-12d3-a456-426614174000"
+    token = create_access_token({"sub": user_id})
+    decoded_payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+
+    assert decoded_payload.get("sub") == user_id
+    assert decoded_payload.get("type") == "access"
+
+
+def test_refresh_token_creation():
+    user_id = "123e4567-e89b-12d3-a456-426614174000"
+    token = create_refresh_token({"sub": user_id})
+    decoded_payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
+
+    assert decoded_payload.get("sub") == user_id
+    assert decoded_payload.get("type") == "refresh"
+
+
+def test_decode_token_valid():
+    user_id = "123e4567-e89b-12d3-a456-426614174000"
+    access_token = create_access_token({"sub": user_id})
+    token_payload = decode_token(access_token)
+
+    assert isinstance(token_payload, TokenPayload)
+    assert token_payload.sub == user_id
+    assert token_payload.type == "access"
+
+
+def test_decode_token_expired():
+    user_id = "123e4567-e89b-12d3-a456-426614174000"
+    token = create_access_token({"sub": user_id}, expires_delta=timedelta(seconds=-1))
+
+    with pytest.raises(JWTError):
+        decode_token(token)
+
+
+def test_decode_token_invalid_signature():
+    token = jwt.encode({"some": "data"}, "invalid_key", algorithm=ALGORITHM)
+    with pytest.raises(JWTError):
+        decode_token(token)
+
+
+def test_decode_token_malformed():
+    malformed_token = "malformed.header.payload"
+    with pytest.raises(JWTError):
+        decode_token(malformed_token)