diff --git a/correlation_id_generation/tests/test_core.py b/correlation_id_generation/tests/test_core.py
new file mode 100644
index 0000000..277ce9f
--- /dev/null
+++ b/correlation_id_generation/tests/test_core.py
@@ -0,0 +1,58 @@
+import json
+import tempfile
+import os
+import time
+import hashlib
+import pytest
+
+from src.correlation_id_generation import core
+
+def test_generate_correlation_id_uniqueness():
+    tgid = 100
+    pid = 200
+    run_seq = 1
+    cid1 = core.generate_correlation_id(tgid, pid, run_seq)
+    cid2 = core.generate_correlation_id(tgid, pid, run_seq + 1)
+    assert isinstance(cid1, str)
+    assert isinstance(cid2, str)
+    assert cid1 != cid2
+
+def test_generate_correlation_id_deterministic_same_input():
+    cid_a = core.generate_correlation_id(1, 2, 3)
+    cid_b = core.generate_correlation_id(1, 2, 3)
+    assert cid_a == cid_b
+
+def test_log_task_state_creates_json_file(tmp_path):
+    log_path = tmp_path / "correlation_log.json"
+    # Patch core's output path in a minimal local context
+    task = "taskA"
+    state_before = "sleeping"
+    state_after = "running"
+    # Generate a correlation id first
+    cid = core.generate_correlation_id(10, 20, 5)
+    # Simulate the internal logging structure manually
+    log_entry = {
+        "correlation_id": cid,
+        "tgid": 10,
+        "pid": 20,
+        "timestamp": pytest.approx(time.time(), abs=2.0),
+        "task": task,
+        "state_before": state_before,
+        "state_after": state_after
+    }
+    # Call the log function, redirecting the output
+    old_cwd = os.getcwd()
+    os.chdir(tmp_path)
+    try:
+        core.log_task_state(task, state_before, state_after)
+        # The log file should now exist
+        stored_file = tmp_path / "output" / "correlation_log.json"
+        assert stored_file.exists()
+        with open(stored_file, "r", encoding="utf-8") as f:
+            data = json.load(f)
+        assert isinstance(data, dict)
+        assert "correlation_id" in data
+        assert isinstance(data["correlation_id"], str)
+        assert "timestamp" in data and isinstance(data["timestamp"], float)
+    finally:
+        os.chdir(old_cwd)