diff --git a/tests/unit/quota/test_quota_exceed_error.py b/tests/unit/quota/test_quota_exceed_error.py
new file mode 100644
index 00000000..b84b29e5
--- /dev/null
+++ b/tests/unit/quota/test_quota_exceed_error.py
@@ -0,0 +1,32 @@
+"""Unit tests for QuotaExceedError class."""
+
+import pytest
+
+from quota.quota_exceed_error import QuotaExceedError
+
+
+def test_quota_exceed_error_constructor():
+    """Test the QuotaExceedError constructor."""
+    expected = "User 1234 has 100 tokens, but 1000 tokens are needed"
+    with pytest.raises(QuotaExceedError, match=expected):
+        raise QuotaExceedError("1234", "u", 100, 1000)
+
+    expected = "Cluster has 100 tokens, but 1000 tokens are needed"
+    with pytest.raises(QuotaExceedError, match=expected):
+        raise QuotaExceedError("", "c", 100, 1000)
+
+    expected = "Unknown subject 1234 has 100 tokens, but 1000 tokens are needed"
+    with pytest.raises(QuotaExceedError, match=expected):
+        raise QuotaExceedError("1234", "?", 100, 1000)
+
+    expected = "User 1234 has no available tokens"
+    with pytest.raises(QuotaExceedError, match=expected):
+        raise QuotaExceedError("1234", "u", 0, 0)
+
+    expected = "Cluster has no available tokens"
+    with pytest.raises(QuotaExceedError, match=expected):
+        raise QuotaExceedError("", "c", 0, 0)
+
+    expected = "Unknown subject 1234 has no available tokens"
+    with pytest.raises(QuotaExceedError, match=expected):
+        raise QuotaExceedError("1234", "?", 0, 0)
diff --git a/tests/unit/quota/test_quota_limiter_factory.py b/tests/unit/quota/test_quota_limiter_factory.py
new file mode 100644
index 00000000..3fc4bd6f
--- /dev/null
+++ b/tests/unit/quota/test_quota_limiter_factory.py
@@ -0,0 +1,204 @@
+"""Unit tests for quota limiter factory class."""
+
+import pytest
+from pytest_mock import MockerFixture
+
+from models.config import (
+    QuotaLimiterConfiguration,
+    PostgreSQLDatabaseConfiguration,
+    SQLiteDatabaseConfiguration,
+    QuotaHandlersConfiguration,
+)
+from quota.cluster_quota_limiter import ClusterQuotaLimiter
+from quota.quota_limiter_factory import QuotaLimiterFactory
+from quota.user_quota_limiter import UserQuotaLimiter
+
+
+def test_quota_limiters_no_storage():
+    """Test the quota limiters creating when no storage is configured."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.sqlite = None
+    configuration.postgres = None
+    configuration.limiters = []
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert limiters == []
+
+
+def test_quota_limiters_no_limiters_pg_storage():
+    """Test the quota limiters creating when no limiters are specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.postgres = PostgreSQLDatabaseConfiguration(
+        db="test", user="user", password="password"
+    )
+    configuration.limiters = None
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert limiters == []
+
+
+def test_quota_limiters_no_limiters_sqlite_storage():
+    """Test the quota limiters creating when no limiters are specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.sqlite = SQLiteDatabaseConfiguration(
+        db_path="/foo/bar",
+    )
+    configuration.limiters = None
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert limiters == []
+
+
+def test_quota_limiters_empty_limiters_pg_storage():
+    """Test the quota limiters creating when no limiters are specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.postgres = PostgreSQLDatabaseConfiguration(
+        db="test", user="user", password="password"
+    )
+    configuration.limiters = []
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert limiters == []
+
+
+def test_quota_limiters_empty_limiters_sqlite_storage():
+    """Test the quota limiters creating when no limiters are specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.sqlite = SQLiteDatabaseConfiguration(
+        db_path="/foo/bar",
+    )
+    configuration.limiters = []
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert limiters == []
+
+
+def test_quota_limiters_user_quota_limiter_postgres_storage(mocker: MockerFixture):
+    """Test the quota limiters creating when one limiter is specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.postgres = PostgreSQLDatabaseConfiguration(
+        db="test", user="user", password="password"
+    )
+    configuration.limiters = [
+        QuotaLimiterConfiguration(
+            type="user_limiter",
+            name="foo",
+            initial_quota=100,
+            quota_increase=1,
+            period="5 days",
+        ),
+    ]
+    # do not use connection to real PostgreSQL instance
+    mocker.patch("psycopg2.connect")
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert len(limiters) == 1
+    assert isinstance(limiters[0], UserQuotaLimiter)
+
+
+def test_quota_limiters_user_quota_limiter_sqlite_storage(mocker: MockerFixture):
+    """Test the quota limiters creating when one limiter is specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.sqlite = SQLiteDatabaseConfiguration(
+        db_path=":memory:",
+    )
+    configuration.limiters = [
+        QuotaLimiterConfiguration(
+            type="user_limiter",
+            name="foo",
+            initial_quota=100,
+            quota_increase=1,
+            period="5 days",
+        ),
+    ]
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert len(limiters) == 1
+    assert isinstance(limiters[0], UserQuotaLimiter)
+
+
+def test_quota_limiters_cluster_quota_limiter_postgres_storage(mocker: MockerFixture):
+    """Test the quota limiters creating when one limiter is specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.postgres = PostgreSQLDatabaseConfiguration(
+        db="test", user="user", password="password"
+    )
+    configuration.limiters = [
+        QuotaLimiterConfiguration(
+            type="cluster_limiter",
+            name="foo",
+            initial_quota=100,
+            quota_increase=1,
+            period="5 days",
+        ),
+    ]
+    # do not use connection to real PostgreSQL instance
+    mocker.patch("psycopg2.connect")
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert len(limiters) == 1
+    assert isinstance(limiters[0], ClusterQuotaLimiter)
+
+
+def test_quota_limiters_cluster_quota_limiter_sqlite_storage(mocker: MockerFixture):
+    """Test the quota limiters creating when one limiter is specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.sqlite = SQLiteDatabaseConfiguration(
+        db_path=":memory:",
+    )
+    configuration.limiters = [
+        QuotaLimiterConfiguration(
+            type="cluster_limiter",
+            name="foo",
+            initial_quota=100,
+            quota_increase=1,
+            period="5 days",
+        ),
+    ]
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert len(limiters) == 1
+    assert isinstance(limiters[0], ClusterQuotaLimiter)
+
+
+def test_quota_limiters_two_limiters(mocker: MockerFixture):
+    """Test the quota limiters creating when two limiters are specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.postgres = PostgreSQLDatabaseConfiguration(
+        db="test", user="user", password="password"
+    )
+    configuration.limiters = [
+        QuotaLimiterConfiguration(
+            type="user_limiter",
+            name="foo",
+            initial_quota=100,
+            quota_increase=1,
+            period="5 days",
+        ),
+        QuotaLimiterConfiguration(
+            type="cluster_limiter",
+            name="foo",
+            initial_quota=100,
+            quota_increase=1,
+            period="5 days",
+        ),
+    ]
+    # do not use connection to real PostgreSQL instance
+    mocker.patch("psycopg2.connect")
+    limiters = QuotaLimiterFactory.quota_limiters(configuration)
+    assert len(limiters) == 2
+    assert isinstance(limiters[0], UserQuotaLimiter)
+    assert isinstance(limiters[1], ClusterQuotaLimiter)
+
+
+def test_quota_limiters_invalid_limiter_type(mocker: MockerFixture):
+    """Test the quota limiters creating when invalid limiter type is specified."""
+    configuration = QuotaHandlersConfiguration()
+    configuration.postgres = PostgreSQLDatabaseConfiguration(
+        db="test", user="user", password="password"
+    )
+    configuration.limiters = [
+        QuotaLimiterConfiguration(
+            type="cluster_limiter",
+            name="foo",
+            initial_quota=100,
+            quota_increase=1,
+            period="5 days",
+        ),
+    ]
+    configuration.limiters[0].type = "foo"
+    # do not use connection to real PostgreSQL instance
+    mocker.patch("psycopg2.connect")
+    with pytest.raises(ValueError, match="Invalid limiter type: foo"):
+        _ = QuotaLimiterFactory.quota_limiters(configuration)