diff --git a/groove/db/manager.py b/groove/db/manager.py
deleted file mode 100644
index 0a50029..0000000
--- a/groove/db/manager.py
+++ /dev/null
@@ -1,43 +0,0 @@
-import os
-
-from sqlalchemy import create_engine
-from sqlalchemy.orm import sessionmaker
-
-from . import metadata
-
-
-class DatabaseManager:
-    """
-    A context manager for working with sqllite database.
-    """
-
-    def __init__(self):
-        self._engine = None
-        self._session = None
-
-    @property
-    def engine(self):
-        if not self._engine:
-            self._engine = create_engine(f"sqlite:///{os.environ.get('DATABASE_PATH')}", future=True)
-        return self._engine
-
-    @property
-    def session(self):
-        if not self._session:
-            Session = sessionmaker(bind=self.engine, future=True)
-            self._session = Session()
-        return self._session
-
-    def import_from_filesystem(self):
-        pass
-
-    def __enter__(self):
-        metadata.create_all(bind=self.engine)
-        return self
-
-    def __exit__(self, exc_type, exc_value, traceback):
-        if self.session:
-            self.session.close()
-
-
-database_manager = DatabaseManager
diff --git a/groove/playlist.py b/groove/playlist.py
index 6d62bdc..d7cec36 100644
--- a/groove/playlist.py
+++ b/groove/playlist.py
@@ -1,6 +1,9 @@
 from groove import db
 from sqlalchemy import func, delete
-from sqlalchemy.exc import NoResultFound
+from sqlalchemy.orm.session import Session
+from sqlalchemy.engine.row import Row
+from sqlalchemy.exc import NoResultFound, MultipleResultsFound
+from typing import Union, List
 import logging
 
 
@@ -8,43 +11,52 @@ class Playlist:
     """
     CRUD operations and convenience methods for playlists.
     """
-    def __init__(self, slug, connection, create_if_not_exists=False):
-        self._conn = connection
+    def __init__(self, slug: str, session: Session, create_if_not_exists: bool = False):
+        self._session = session
         self._slug = slug
         self._record = None
         self._entries = None
         self._create_if_not_exists = create_if_not_exists
 
     @property
-    def exists(self):
+    def exists(self) -> bool:
+        """
+        True if the playlist exists in the database.
+        """
         return self.record is not None
 
     @property
-    def slug(self):
+    def slug(self) -> Union[str, None]:
         return self._slug
 
     @property
-    def conn(self):
-        return self._conn
+    def session(self) -> Union[Session, None]:
+        return self._session
 
     @property
-    def record(self):
+    def record(self) -> Union[Row, None]:
+        """
+        Cache the playlist row from the database and return it. Optionally create it if it doesn't exist.
+        """
         if not self._record:
             try:
-                self._record = self.conn.query(db.playlist).filter(db.playlist.c.slug == self.slug).one()
+                self._record = self.session.query(db.playlist).filter(db.playlist.c.slug == self.slug).one()
                 logging.debug(f"Retrieved playlist {self._record.id}")
             except NoResultFound:
                 pass
             if self._create_if_not_exists:
                 self._record = self._create()
-                if not self._record:
+                if not self._record:  # pragma: no cover
                     raise RuntimeError(f"Tried to create a playlist but couldn't read it back using slug {self.slug}")
         return self._record
 
     @property
-    def entries(self):
-        if not self._entries:
-            self._entries = self.conn.query(
+    def entries(self) -> Union[List, None]:
+        """
+        Cache the list of entries on this playlist and return it.
+        """
+        if not self._entries and self.record:
+            self._entries = self.session.query(
                 db.entry,
                 db.track
             ).filter(
@@ -59,46 +71,87 @@ class Playlist:
     @property
     def as_dict(self) -> dict:
         """
-        Retrieve a playlist and its entries by its slug.
+        Return a dictionary of the playlist and its entries.
         """
-        playlist = {}
+        if not self.record:
+            return {}
         playlist = dict(self.record)
         playlist['entries'] = [dict(entry) for entry in self.entries]
         return playlist
 
-    def add(self, paths) -> int:
-        return self._create_entries(self._get_tracks_by_path(paths))
+    def add(self, paths: List[str]) -> int:
+        """
+        Add entries to the playlist.  Each path should match one and only one track in the database (case-insensitive).
+        If a path doesn't match any track, or if a path matches multiple tracks, nothing is added to the playlist.
 
-    def delete(self):
+        Args:
+            paths (list): A list of partial paths to add.
+
+        Returns:
+            int: The number of tracks added.
+        """
+        try:
+            return self._create_entries(self._get_tracks_by_path(paths))
+        except NoResultFound:
+            logging.error("One or more of the specified paths do not match any tracks in the database.")
+            return 0
+        except MultipleResultsFound:
+            logging.error("One or more of the specified paths matches multiple tracks in the database.")
+            return 0
+
+    def delete(self) -> Union[int, None]:
+        """
+        Delete a playlist and its entries from the database, then clear the cached values.
+        """
+        if not self.record:
+            return None
         plid = self.record.id
         stmt = delete(db.entry).where(db.entry.c.playlist_id == plid)
         logging.debug(f"Deleting entries associated with playlist {plid}: {stmt}")
-        self.conn.execute(stmt)
+        self.session.execute(stmt)
         stmt = delete(db.playlist).where(db.playlist.c.id == plid)
         logging.debug(f"Deleting playlist {plid}: {stmt}")
-        self.conn.execute(stmt)
-        self.conn.commit()
+        self.session.execute(stmt)
+        self.session.commit()
+        self._record = None
+        self._entries = None
         return plid
 
-    def _get_tracks_by_path(self, paths):
-        return [self.conn.query(db.track).filter(db.track.c.relpath.ilike(f"%{path}%")).one() for path in paths]
+    def _get_tracks_by_path(self, paths: List[str]) -> List:
+        """
+        Retrieve tracks from the database that match the specified path fragments. The exceptions NoResultFound and
+        MultipleResultsFound are expected in the case of no matches and multiple matches, respectively.
+        """
+        return [self.session.query(db.track).filter(db.track.c.relpath.ilike(f"%{path}%")).one() for path in paths]
 
-    def _create_entries(self, tracks):
+    def _create_entries(self, tracks: List[Row]) -> int:
+        """
+        Append a list of tracks to a playlist by populating the entries table with records referencing the playlist and
+        the specified tracks.
 
-        maxtrack = self.conn.query(func.max(db.entry.c.track)).filter_by(playlist_id=self.record.id).one()[0]
-        self.conn.execute(
+        Args:
+            tracks (list): A list of Row objects from the track table.
+
+        Returns:
+            int: The number of tracks added.
+        """
+        maxtrack = self.session.query(func.max(db.entry.c.track)).filter_by(playlist_id=self.record.id).one()[0] or 0
+        self.session.execute(
             db.entry.insert(),
             [
                 {'playlist_id': self.record.id, 'track_id': obj.id, 'track': idx}
                 for (idx, obj) in enumerate(tracks, start=maxtrack+1)
             ]
         )
-        self.conn.commit()
+        self.session.commit()
         return len(tracks)
 
-    def _create(self):
+    def _create(self) -> Row:
+        """
+        Insert a new playlist record into the database.
+        """
         stmt = db.playlist.insert({'slug': self.slug})
-        results = self.conn.execute(stmt)
-        self.conn.commit()
-        logging.debug(f"Created new playlist {results.inserted_primary_key} with slug {self.slug}")
-        return self.conn.query(db.playlist).filter(db.playlist.c.id == results.inserted_primary_key).one()
+        results = self.session.execute(stmt)
+        self.session.commit()
+        logging.debug(f"Created new playlist {results.inserted_primary_key[0]} with slug {self.slug}")
+        return self.session.query(db.playlist).filter(db.playlist.c.id == results.inserted_primary_key[0]).one()
diff --git a/groove/webserver.py b/groove/webserver.py
index 3867e27..deb54a4 100644
--- a/groove/webserver.py
+++ b/groove/webserver.py
@@ -45,7 +45,7 @@ def get_playlist(slug, db):
     Retrieve a playlist and its entries by a slug.
     """
     logging.debug(f"Looking up playlist: {slug}...")
-    playlist = Playlist(slug=slug, conn=db)
+    playlist = Playlist(slug=slug, session=db)
     if not playlist.exists:
         return HTTPResponse(status=404, body="Not found")
     response = json.dumps(playlist.as_dict)
diff --git a/test/conftest.py b/test/conftest.py
index a075d1d..5a7fa7a 100644
--- a/test/conftest.py
+++ b/test/conftest.py
@@ -38,7 +38,8 @@ def db(in_memory_db):
     in_memory_db.execute(query, [
         {'id': 1, 'name': 'playlist one', 'description': 'the first one', 'slug': 'playlist-one'},
         {'id': 2, 'name': 'playlist two', 'description': 'the second one', 'slug': 'playlist-two'},
-        {'id': 3, 'name': 'playlist three', 'description': 'the threerd one', 'slug': 'playlist-three'}
+        {'id': 3, 'name': 'playlist three', 'description': 'the threerd one', 'slug': 'playlist-three'},
+        {'id': 4, 'name': 'empty playlist', 'description': 'no tracks', 'slug': 'empty-playlist'}
     ])
 
     # populate the playlists
diff --git a/test/test_playlists.py b/test/test_playlists.py
index 3b047bb..f3ae1ed 100644
--- a/test/test_playlists.py
+++ b/test/test_playlists.py
@@ -1,12 +1,48 @@
+# 70, 73-81, 84, 88-97, 100-104
+import pytest
+from groove import playlist
 
 
-def test_create_playlist():
-    pass
+def test_create(db):
+    pl = playlist.Playlist(slug='test-create-playlist', session=db, create_if_not_exists=True)
+    assert pl.exists
 
 
-def test_update_playlist():
-    pass
+@pytest.mark.parametrize('tracks', [
+    ('01 Guns Blazing', ),
+    ('01 Guns Blazing', '02 UNKLE'),
+])
+def test_add(db, tracks):
+    pl = playlist.Playlist(slug='test-create-playlist', session=db, create_if_not_exists=True)
+    count = pl.add(tracks)
+    assert count == len(tracks)
 
 
-def delete_playlist():
-    pass
+def test_add_no_matches(db):
+    pl = playlist.Playlist(slug='playlist-one', session=db)
+    assert pl.add(('no match', )) == 0
+
+
+def test_add_multiple_matches(db):
+    pl = playlist.Playlist(slug='playlist-one', session=db)
+    assert pl.add('UNKLE',) == 0
+
+
+def test_delete(db):
+    pl = playlist.Playlist(slug='playlist-one', session=db)
+    expected = pl.record.id
+    assert pl.delete() == expected
+    assert not pl.as_dict
+
+
+def test_delete_playlist_not_exist(db):
+    pl = playlist.Playlist(slug='playlist-doesnt-exist', session=db)
+    assert not pl.delete()
+    assert not pl.as_dict
+
+
+def test_entries(db):
+    pl = playlist.Playlist(slug='playlist-one', session=db)
+    # assert twice for branch coverage of cached values
+    assert pl.entries
+    assert pl.entries
diff --git a/test/test_scanner.py b/test/test_scanner.py
index 227e9fa..7e45274 100644
--- a/test/test_scanner.py
+++ b/test/test_scanner.py
@@ -1,4 +1,5 @@
 import pytest
+import os
 from pathlib import Path
 from unittest.mock import MagicMock
 from sqlalchemy import func
@@ -47,3 +48,9 @@ def test_scanner(monkeypatch, in_memory_db, media):
 
     # verify idempotency
     assert test_scanner.scan() == 0
+
+
+def test_scanner_no_media_root(in_memory_db):
+    del os.environ['MEDIA_ROOT']
+    with pytest.raises(SystemExit):
+        assert scanner.media_scanner(root=None, db=in_memory_db)