diff --git a/tests/test_storage.py b/tests/test_storage.py
new file mode 100644
index 0000000..541f5c0
--- /dev/null
+++ b/tests/test_storage.py
@@ -0,0 +1,88 @@
+"""Test cases for the Storage class."""
+import unittest
+import os
+import numpy as np
+from pysentence_similarity._storage import Storage, InvalidDataError
+
+
+class TestStorage(unittest.TestCase):
+    """Test cases for the Storage class."""
+
+    def setUp(self) -> None:
+        """Set up test data before each test."""
+        self.sentences = [
+            "This is a test sentence.",
+            "This is another sentence."
+        ]
+        self.embeddings = [np.random.rand(3), np.random.rand(3)]
+        self.storage = Storage(
+            sentences=self.sentences,
+            embeddings=self.embeddings
+        )
+        self.test_filename = "test_storage.h5"
+
+    def tearDown(self) -> None:
+        """Remove test file after each test."""
+        if os.path.exists(self.test_filename):
+            os.remove(self.test_filename)
+
+    def test_initialization_valid(self) -> None:
+        """Test initialization with valid data."""
+        self.assertEqual(len(self.storage), 2)
+        self.assertEqual(self.storage._sentences, self.sentences)
+
+    def test_initialization_invalid_sentences(self) -> None:
+        """Test initialization with invalid sentences."""
+        with self.assertRaises(InvalidDataError):
+            Storage(sentences="Not a list", embeddings=self.embeddings)
+
+    def test_initialization_invalid_embeddings(self) -> None:
+        """Test initialization with invalid embeddings."""
+        with self.assertRaises(InvalidDataError):
+            Storage(sentences=self.sentences, embeddings="Not a list")
+
+    def test_save_and_load(self) -> None:
+        """Test saving and loading data."""
+        self.storage.save(self.test_filename)
+        loaded_storage = Storage.load(self.test_filename)
+        self.assertEqual(len(loaded_storage), 2)
+        self.assertEqual(loaded_storage._sentences, self.sentences)
+
+    def test_save_invalid_data(self) -> None:
+        """Test saving with invalid data."""
+        self.storage._sentences.append(123)
+        with self.assertRaises(InvalidDataError):
+            self.storage.save(self.test_filename)
+
+    def test_add_sentences_and_embeddings(self) -> None:
+        """Test adding valid sentences and embeddings."""
+        new_sentence = "This is a new sentence."
+        new_embedding = np.random.rand(3)
+        self.storage.add(new_sentence, new_embedding)
+
+        self.assertEqual(len(self.storage), 3)
+        self.assertEqual(self.storage._sentences[-1], new_sentence)
+
+    def test_add_and_save(self) -> None:
+        """Test adding and saving."""
+        new_sentence = "This is another new sentence."
+        new_embedding = np.random.rand(3)
+        self.storage.add(
+            new_sentence,
+            new_embedding,
+            save=True,
+            filename=self.test_filename
+        )
+
+        loaded_storage = Storage.load(self.test_filename)
+        self.assertEqual(len(loaded_storage), 3)
+        self.assertEqual(loaded_storage._sentences[-1], new_sentence)
+
+    def test_index_out_of_range(self) -> None:
+        """Test index out of range."""
+        with self.assertRaises(IndexError):
+            self.storage[10]
+
+
+if __name__ == "__main__":
+    unittest.main()