diff --git a/tests/app/test_app_actions_selection_and_controls.py b/tests/app/test_app_actions_selection_and_controls.py
new file mode 100644
index 0000000..d708eff
--- /dev/null
+++ b/tests/app/test_app_actions_selection_and_controls.py
@@ -0,0 +1,124 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from auditui.app.actions import AppActionsMixin
+
+
+@dataclass(slots=True)
+class FakeTable:
+    """Minimal table shim exposing cursor and row count."""
+
+    row_count: int
+    cursor_row: int = 0
+
+
+class FakePlayback:
+    """Playback stub with togglable boolean return values."""
+
+    def __init__(self, result: bool) -> None:
+        """Store deterministic toggle result for tests."""
+        self._result = result
+        self.calls: list[str] = []
+
+    def toggle_playback(self) -> bool:
+        """Return configured result and record call."""
+        self.calls.append("toggle")
+        return self._result
+
+    def seek_forward(self, _seconds: float) -> bool:
+        """Return configured result and record call."""
+        self.calls.append("seek_forward")
+        return self._result
+
+
+class DummyActionsApp(AppActionsMixin):
+    """Mixin host with just enough state for action method tests."""
+
+    def __init__(self) -> None:
+        """Initialize fake app state used by action helpers."""
+        self.messages: list[str] = []
+        self.current_items: list[dict] = []
+        self.download_manager = object()
+        self.library_client = type(
+            "Library", (), {"extract_asin": lambda self, item: item.get("asin")}
+        )()
+        self.playback = FakePlayback(True)
+        self.filter_text = "hello"
+        self._refreshed = 0
+        self._table = FakeTable(row_count=0, cursor_row=0)
+
+    def update_status(self, message: str) -> None:
+        """Collect status messages for assertions."""
+        self.messages.append(message)
+
+    def query_one(self, selector: str, _type: object) -> FakeTable:
+        """Return the fake table used in selection tests."""
+        assert selector == "#library_table"
+        return self._table
+
+    def _refresh_filtered_view(self) -> None:
+        """Record refresh invocations for filter tests."""
+        self._refreshed += 1
+
+    def _start_playback_async(self, asin: str) -> None:
+        """Capture async playback launch argument."""
+        self.messages.append(f"start:{asin}")
+
+
+def test_get_selected_asin_requires_non_empty_table() -> None:
+    """Ensure selection fails gracefully when table has no rows."""
+    app = DummyActionsApp()
+    app._table = FakeTable(row_count=0)
+    assert app._get_selected_asin() is None
+    assert app.messages[-1] == "No books available"
+
+
+def test_get_selected_asin_returns_current_row_asin() -> None:
+    """Ensure selected row index maps to current_items ASIN."""
+    app = DummyActionsApp()
+    app._table = FakeTable(row_count=2, cursor_row=1)
+    app.current_items = [{"asin": "A1"}, {"asin": "A2"}]
+    assert app._get_selected_asin() == "A2"
+
+
+def test_action_play_selected_starts_async_playback() -> None:
+    """Ensure play action calls async starter with selected ASIN."""
+    app = DummyActionsApp()
+    app._table = FakeTable(row_count=1, cursor_row=0)
+    app.current_items = [{"asin": "ASIN"}]
+    app.action_play_selected()
+    assert app.messages[-1] == "start:ASIN"
+
+
+def test_action_toggle_playback_shows_hint_when_no_playback() -> None:
+    """Ensure toggle action displays no-playback hint on false return."""
+    app = DummyActionsApp()
+    app.playback = FakePlayback(False)
+    app.action_toggle_playback()
+    assert app.messages[-1] == "No playback active. Press Enter to play a book."
+
+
+def test_action_seek_forward_shows_hint_when_seek_fails() -> None:
+    """Ensure failed seek action reuses no-playback helper status."""
+    app = DummyActionsApp()
+    app.playback = FakePlayback(False)
+    app.action_seek_forward()
+    assert app.messages[-1] == "No playback active. Press Enter to play a book."
+
+
+def test_action_clear_filter_resets_filter_and_refreshes() -> None:
+    """Ensure clearing filter resets text and refreshes filtered view."""
+    app = DummyActionsApp()
+    app.action_clear_filter()
+    assert app.filter_text == ""
+    assert app._refreshed == 1
+    assert app.messages[-1] == "Filter cleared"
+
+
+def test_apply_filter_coerces_none_to_empty_string() -> None:
+    """Ensure apply_filter normalizes None and refreshes list view."""
+    app = DummyActionsApp()
+    app._apply_filter(None)
+    assert app.filter_text == ""
+    assert app._refreshed == 1
diff --git a/tests/app/test_app_library_mixin_behavior.py b/tests/app/test_app_library_mixin_behavior.py
new file mode 100644
index 0000000..cab782e
--- /dev/null
+++ b/tests/app/test_app_library_mixin_behavior.py
@@ -0,0 +1,114 @@
+from __future__ import annotations
+
+from auditui.app.library import AppLibraryMixin
+from auditui.app import library as library_mod
+
+
+class DummyLibraryApp(AppLibraryMixin):
+    """Mixin host exposing only members used by AppLibraryMixin."""
+
+    def __init__(self) -> None:
+        """Initialize in-memory app state and call tracking."""
+        self.all_items: list[dict] = []
+        self.show_all_mode = False
+        self._search_text_cache: dict[int, str] = {1: "x"}
+        self.messages: list[str] = []
+        self.call_log: list[tuple[str, tuple]] = []
+        self.library_client = None
+
+    def _prime_search_cache(self, items: list[dict]) -> None:
+        """Store a marker so callers can assert this method was reached."""
+        self.call_log.append(("prime", (items,)))
+
+    def show_all(self) -> None:
+        """Record show_all invocation for assertion."""
+        self.call_log.append(("show_all", ()))
+
+    def show_unfinished(self) -> None:
+        """Record show_unfinished invocation for assertion."""
+        self.call_log.append(("show_unfinished", ()))
+
+    def update_status(self, message: str) -> None:
+        """Capture status messages."""
+        self.messages.append(message)
+
+    def call_from_thread(self, func, *args) -> None:
+        """Execute callback immediately to simplify tests."""
+        func(*args)
+
+    def _thread_status_update(self, message: str) -> None:
+        """Capture worker-thread status update messages."""
+        self.messages.append(message)
+
+
+def test_on_library_loaded_refreshes_cache_and_shows_unfinished() -> None:
+    """Ensure loaded items reset cache and default to unfinished view."""
+    app = DummyLibraryApp()
+    items = [{"asin": "a"}, {"asin": "b"}]
+    app.on_library_loaded(items)
+    assert app.all_items == items
+    assert app._search_text_cache == {}
+    assert app.messages[-1] == "Loaded 2 books"
+    assert app.call_log[-1][0] == "show_unfinished"
+
+
+def test_on_library_loaded_uses_show_all_mode() -> None:
+    """Ensure loaded items respect show_all mode when enabled."""
+    app = DummyLibraryApp()
+    app.show_all_mode = True
+    app.on_library_loaded([{"asin": "a"}])
+    assert app.call_log[-1][0] == "show_all"
+
+
+def test_on_library_error_formats_message() -> None:
+    """Ensure library errors are surfaced through status updates."""
+    app = DummyLibraryApp()
+    app.on_library_error("boom")
+    assert app.messages == ["Error fetching library: boom"]
+
+
+def test_fetch_library_calls_on_loaded(monkeypatch) -> None:
+    """Ensure fetch_library forwards fetched items through call_from_thread."""
+    app = DummyLibraryApp()
+
+    class Worker:
+        """Simple worker shim exposing cancellation state."""
+
+        is_cancelled = False
+
+    class LibraryClient:
+        """Fake client returning a deterministic item list."""
+
+        def fetch_all_items(self, callback):
+            """Invoke callback and return one item."""
+            callback("progress")
+            return [{"asin": "x"}]
+
+    app.library_client = LibraryClient()
+    monkeypatch.setattr(library_mod, "get_current_worker", lambda: Worker())
+    AppLibraryMixin.fetch_library.__wrapped__(app)
+    assert app.all_items == [{"asin": "x"}]
+    assert "Loaded 1 books" in app.messages
+
+
+def test_fetch_library_handles_expected_exception(monkeypatch) -> None:
+    """Ensure fetch exceptions call on_library_error with error text."""
+    app = DummyLibraryApp()
+
+    class Worker:
+        """Simple worker shim exposing cancellation state."""
+
+        is_cancelled = False
+
+    class BrokenClient:
+        """Fake client raising an expected fetch exception."""
+
+        def fetch_all_items(self, callback):
+            """Raise the same exception family handled by mixin."""
+            del callback
+            raise ValueError("bad fetch")
+
+    app.library_client = BrokenClient()
+    monkeypatch.setattr(library_mod, "get_current_worker", lambda: Worker())
+    AppLibraryMixin.fetch_library.__wrapped__(app)
+    assert app.messages[-1] == "Error fetching library: bad fetch"
diff --git a/tests/app/test_app_progress_mixin_behavior.py b/tests/app/test_app_progress_mixin_behavior.py
new file mode 100644
index 0000000..1e095bb
--- /dev/null
+++ b/tests/app/test_app_progress_mixin_behavior.py
@@ -0,0 +1,148 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import cast
+
+from auditui.app.progress import AppProgressMixin
+from textual.events import Key
+from textual.widgets import DataTable
+
+
+@dataclass(slots=True)
+class FakeKeyEvent:
+    """Minimal key event carrying key value and prevent_default state."""
+
+    key: str
+    prevented: bool = False
+
+    def prevent_default(self) -> None:
+        """Mark event as prevented."""
+        self.prevented = True
+
+
+@dataclass(slots=True)
+class FakeStatic:
+    """Minimal static widget with text and visibility fields."""
+
+    display: bool = False
+    text: str = ""
+
+    def update(self, value: str) -> None:
+        """Store rendered text value."""
+        self.text = value
+
+
+@dataclass(slots=True)
+class FakeProgressBar:
+    """Minimal progress bar widget storing latest progress value."""
+
+    progress: float = 0.0
+
+    def update(self, progress: float) -> None:
+        """Store progress value for assertions."""
+        self.progress = progress
+
+
+@dataclass(slots=True)
+class FakeContainer:
+    """Minimal container exposing display property."""
+
+    display: bool = False
+
+
+class DummyPlayback:
+    """Playback shim exposing only members used by AppProgressMixin."""
+
+    def __init__(self) -> None:
+        """Initialize playback state and update counters."""
+        self.is_playing = False
+        self._status: str | None = None
+        self._progress: tuple[str, float, float] | None = None
+        self.saved_calls = 0
+
+    def check_status(self):
+        """Return configurable status check message."""
+        return self._status
+
+    def get_current_progress(self):
+        """Return configurable progress tuple."""
+        return self._progress
+
+    def update_position_if_needed(self) -> None:
+        """Record periodic save invocations."""
+        self.saved_calls += 1
+
+
+class DummyProgressApp(AppProgressMixin):
+    """Mixin host that records action dispatch and widget updates."""
+
+    def __init__(self) -> None:
+        """Initialize fake widgets and playback state."""
+        self.playback = DummyPlayback()
+        self.focused = object()
+        self.actions: list[str] = []
+        self.messages: list[str] = []
+        self.progress_info = FakeStatic()
+        self.progress_bar = FakeProgressBar()
+        self.progress_container = FakeContainer()
+
+    def action_seek_backward(self) -> None:
+        """Record backward seek action dispatch."""
+        self.actions.append("seek_backward")
+
+    def action_toggle_playback(self) -> None:
+        """Record toggle playback action dispatch."""
+        self.actions.append("toggle")
+
+    def update_status(self, message: str) -> None:
+        """Capture status messages for assertions."""
+        self.messages.append(message)
+
+    def query_one(self, selector: str, _type: object):
+        """Return fake widgets by selector used by progress mixin."""
+        return {
+            "#progress_info": self.progress_info,
+            "#progress_bar": self.progress_bar,
+            "#progress_bar_container": self.progress_container,
+        }[selector]
+
+
+def test_on_key_dispatches_seek_when_playing() -> None:
+    """Ensure left key is intercepted and dispatched to seek action."""
+    app = DummyProgressApp()
+    app.playback.is_playing = True
+    event = FakeKeyEvent("left")
+    app.on_key(cast(Key, event))
+    assert event.prevented is True
+    assert app.actions == ["seek_backward"]
+
+
+def test_on_key_dispatches_space_when_table_focused() -> None:
+    """Ensure space is intercepted and dispatched when table is focused."""
+    app = DummyProgressApp()
+    app.focused = DataTable()
+    event = FakeKeyEvent("space")
+    app.on_key(cast(Key, event))
+    assert event.prevented is True
+    assert app.actions == ["toggle"]
+
+
+def test_check_playback_status_hides_progress_after_message() -> None:
+    """Ensure playback status message triggers hide-progress behavior."""
+    app = DummyProgressApp()
+    app.playback._status = "Finished"
+    app._check_playback_status()
+    assert app.messages[-1] == "Finished"
+    assert app.progress_info.display is False
+    assert app.progress_container.display is False
+
+
+def test_update_progress_renders_visible_progress_row() -> None:
+    """Ensure valid progress data updates widgets and makes them visible."""
+    app = DummyProgressApp()
+    app.playback.is_playing = True
+    app.playback._progress = ("Chapter", 30.0, 60.0)
+    app._update_progress()
+    assert app.progress_bar.progress == 50.0
+    assert app.progress_info.display is True
+    assert app.progress_container.display is True
diff --git a/tests/app/test_app_progress_periodic_save.py b/tests/app/test_app_progress_periodic_save.py
new file mode 100644
index 0000000..77bc072
--- /dev/null
+++ b/tests/app/test_app_progress_periodic_save.py
@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+from auditui.app.progress import AppProgressMixin
+
+
+class DummyPlayback:
+    """Playback stub exposing periodic update method."""
+
+    def __init__(self) -> None:
+        """Initialize call counter."""
+        self.saved_calls = 0
+
+    def update_position_if_needed(self) -> None:
+        """Increment call counter for assertions."""
+        self.saved_calls += 1
+
+
+class DummyProgressApp(AppProgressMixin):
+    """Minimal app host containing playback dependency only."""
+
+    def __init__(self) -> None:
+        """Initialize playback stub."""
+        self.playback = DummyPlayback()
+
+
+def test_save_position_periodically_delegates_to_playback() -> None:
+    """Ensure periodic save method delegates to playback updater."""
+    app = DummyProgressApp()
+    app._save_position_periodically()
+    assert app.playback.saved_calls == 1
diff --git a/tests/app/test_app_state_initialization.py b/tests/app/test_app_state_initialization.py
new file mode 100644
index 0000000..b102001
--- /dev/null
+++ b/tests/app/test_app_state_initialization.py
@@ -0,0 +1,78 @@
+from __future__ import annotations
+
+from auditui.app import state as state_mod
+
+
+class DummyApp:
+    """Lightweight app object for state initialization tests."""
+
+    def __init__(self) -> None:
+        """Expose update_status to satisfy init dependencies."""
+        self.messages: list[str] = []
+
+    def update_status(self, message: str) -> None:
+        """Collect status updates for assertions."""
+        self.messages.append(message)
+
+
+def test_init_state_without_auth_or_client(monkeypatch) -> None:
+    """Ensure baseline state is initialized when no auth/client is provided."""
+    app = DummyApp()
+    playback_args: list[tuple[object, object]] = []
+
+    class FakePlayback:
+        """Playback constructor recorder for init tests."""
+
+        def __init__(self, notify, library_client) -> None:
+            """Capture arguments passed by init_auditui_state."""
+            playback_args.append((notify, library_client))
+
+    monkeypatch.setattr(state_mod, "PlaybackController", FakePlayback)
+    state_mod.init_auditui_state(app)
+    assert app.library_client is None
+    assert app.download_manager is None
+    assert app.all_items == []
+    assert app.current_items == []
+    assert app.filter_text == ""
+    assert app.show_all_mode is False
+    assert playback_args and playback_args[0][1] is None
+
+
+def test_init_state_with_auth_and_client_builds_dependencies(monkeypatch) -> None:
+    """Ensure init constructs library, downloads, and playback dependencies."""
+    app = DummyApp()
+    auth = object()
+    client = object()
+
+    class FakeLibraryClient:
+        """Fake library client constructor for dependency wiring checks."""
+
+        def __init__(self, value) -> None:
+            """Store constructor argument for assertions."""
+            self.value = value
+
+    class FakeDownloadManager:
+        """Fake download manager constructor for dependency wiring checks."""
+
+        def __init__(self, auth_value, client_value) -> None:
+            """Store constructor arguments for assertions."""
+            self.args = (auth_value, client_value)
+
+    class FakePlayback:
+        """Fake playback constructor for dependency wiring checks."""
+
+        def __init__(self, notify, library_client) -> None:
+            """Store constructor arguments for assertions."""
+            self.notify = notify
+            self.library_client = library_client
+
+    monkeypatch.setattr(state_mod, "LibraryClient", FakeLibraryClient)
+    monkeypatch.setattr(state_mod, "DownloadManager", FakeDownloadManager)
+    monkeypatch.setattr(state_mod, "PlaybackController", FakePlayback)
+    state_mod.init_auditui_state(app, auth=auth, client=client)
+    assert isinstance(app.library_client, FakeLibraryClient)
+    assert isinstance(app.download_manager, FakeDownloadManager)
+    assert isinstance(app.playback, FakePlayback)
+    assert app.library_client.value is client
+    assert app.download_manager.args == (auth, client)
+    assert app.playback.library_client.value is client
diff --git a/tests/playback/test_playback_controller_lifecycle_mixin.py b/tests/playback/test_playback_controller_lifecycle_mixin.py
new file mode 100644
index 0000000..db9cc38
--- /dev/null
+++ b/tests/playback/test_playback_controller_lifecycle_mixin.py
@@ -0,0 +1,121 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+from auditui.playback import controller_lifecycle as lifecycle_mod
+from auditui.playback.controller import PlaybackController
+
+
+class Proc:
+    """Process shim used for lifecycle tests."""
+
+    def __init__(self, poll_value=None) -> None:
+        """Set initial poll result."""
+        self._poll_value = poll_value
+
+    def poll(self):
+        """Return process running status."""
+        return self._poll_value
+
+
+def _controller() -> tuple[PlaybackController, list[str]]:
+    """Build controller and message capture list."""
+    messages: list[str] = []
+    return PlaybackController(messages.append, None), messages
+
+
+def test_start_reports_missing_ffplay(monkeypatch) -> None:
+    """Ensure start fails fast when ffplay is unavailable."""
+    controller, messages = _controller()
+    monkeypatch.setattr(lifecycle_mod.process_mod, "is_ffplay_available", lambda: False)
+    assert controller.start(Path("book.aax")) is False
+    assert messages[-1] == "ffplay not found. Please install ffmpeg"
+
+
+def test_start_sets_state_on_success(monkeypatch) -> None:
+    """Ensure successful start initializes playback state and metadata."""
+    controller, messages = _controller()
+    monkeypatch.setattr(lifecycle_mod.process_mod, "is_ffplay_available", lambda: True)
+    monkeypatch.setattr(
+        lifecycle_mod.process_mod, "build_ffplay_cmd", lambda *args: ["ffplay"]
+    )
+    monkeypatch.setattr(
+        lifecycle_mod.process_mod, "run_ffplay", lambda cmd: (Proc(None), None)
+    )
+    monkeypatch.setattr(
+        lifecycle_mod,
+        "load_media_info",
+        lambda path, activation: (600.0, [{"title": "ch"}]),
+    )
+    monkeypatch.setattr(lifecycle_mod.time, "time", lambda: 100.0)
+    ok = controller.start(
+        Path("book.aax"), activation_hex="abcd", start_position=10.0, speed=1.2
+    )
+    assert ok is True
+    assert controller.is_playing is True
+    assert controller.current_file_path == Path("book.aax")
+    assert controller.total_duration == 600.0
+    assert messages[-1] == "Playing: book.aax"
+
+
+def test_prepare_and_start_uses_last_position(monkeypatch) -> None:
+    """Ensure prepare flow resumes from saved position when available."""
+    messages: list[str] = []
+    lib = type("Lib", (), {"get_last_position": lambda self, asin: 75.0})()
+    controller = PlaybackController(messages.append, lib)
+    started: list[tuple] = []
+
+    class DM:
+        """Download manager shim returning path and activation token."""
+
+        def get_or_download(self, asin, notify):
+            """Return deterministic downloaded file path."""
+            return Path("book.aax")
+
+        def get_activation_bytes(self):
+            """Return deterministic activation token."""
+            return "abcd"
+
+    monkeypatch.setattr(controller, "start", lambda *args: started.append(args) or True)
+    monkeypatch.setattr(lifecycle_mod.time, "time", lambda: 200.0)
+    assert controller.prepare_and_start(DM(), "ASIN") is True
+    assert started and started[0][3] == 75.0
+    assert "Resuming from 01:15" in messages
+
+
+def test_toggle_playback_uses_pause_and_resume_paths(monkeypatch) -> None:
+    """Ensure toggle dispatches pause or resume based on paused flag."""
+    controller, _ = _controller()
+    controller.is_playing = True
+    controller.playback_process = Proc(None)
+    called: list[str] = []
+    monkeypatch.setattr(controller, "pause", lambda: called.append("pause"))
+    monkeypatch.setattr(controller, "resume", lambda: called.append("resume"))
+    controller.is_paused = False
+    assert controller.toggle_playback() is True
+    controller.is_paused = True
+    assert controller.toggle_playback() is True
+    assert called == ["pause", "resume"]
+
+
+def test_restart_at_position_restores_state_and_notifies(monkeypatch) -> None:
+    """Ensure restart logic preserves metadata and emits custom message."""
+    controller, messages = _controller()
+    controller.is_playing = True
+    controller.is_paused = True
+    controller.current_file_path = Path("book.aax")
+    controller.current_asin = "ASIN"
+    controller.activation_hex = "abcd"
+    controller.total_duration = 400.0
+    controller.chapters = [{"title": "One"}]
+    controller.playback_speed = 1.0
+    monkeypatch.setattr(controller, "_stop_process", lambda: None)
+    monkeypatch.setattr(lifecycle_mod.time, "sleep", lambda _s: None)
+    monkeypatch.setattr(controller, "start", lambda *args: True)
+    paused: list[str] = []
+    monkeypatch.setattr(controller, "pause", lambda: paused.append("pause"))
+    assert controller._restart_at_position(120.0, message="Jumped") is True
+    assert controller.current_asin == "ASIN"
+    assert controller.chapters == [{"title": "One"}]
+    assert paused == ["pause"]
+    assert messages[-1] == "Jumped"
diff --git a/tests/playback/test_playback_controller_seek_speed_mixin.py b/tests/playback/test_playback_controller_seek_speed_mixin.py
new file mode 100644
index 0000000..1567d88
--- /dev/null
+++ b/tests/playback/test_playback_controller_seek_speed_mixin.py
@@ -0,0 +1,100 @@
+from __future__ import annotations
+
+from auditui.playback import controller_seek_speed as seek_speed_mod
+from auditui.playback.controller import PlaybackController
+
+
+def _controller() -> tuple[PlaybackController, list[str]]:
+    """Build controller and in-memory notification sink."""
+    messages: list[str] = []
+    return PlaybackController(messages.append, None), messages
+
+
+def test_seek_notifies_when_target_invalid(monkeypatch) -> None:
+    """Ensure seek reports end-of-file condition when target is invalid."""
+    controller, messages = _controller()
+    monkeypatch.setattr(controller, "_get_current_elapsed", lambda: 20.0)
+    controller.seek_offset = 100.0
+    controller.total_duration = 120.0
+    monkeypatch.setattr(
+        seek_speed_mod.seek_mod, "compute_seek_target", lambda *args: None
+    )
+    assert controller._seek(30.0, "forward") is False
+    assert messages[-1] == "Already at end of file"
+
+
+def test_seek_to_chapter_reports_bounds(monkeypatch) -> None:
+    """Ensure chapter seek reports first and last chapter boundaries."""
+    controller, messages = _controller()
+    controller.is_playing = True
+    controller.current_file_path = object()
+    controller.chapters = [{"title": "One", "start_time": 0.0, "end_time": 10.0}]
+    monkeypatch.setattr(controller, "_get_current_elapsed", lambda: 1.0)
+    monkeypatch.setattr(
+        seek_speed_mod.chapters_mod,
+        "get_current_chapter_index",
+        lambda elapsed, chapters: 0,
+    )
+    assert controller.seek_to_chapter("next") is False
+    assert messages[-1] == "Already at last chapter"
+    assert controller.seek_to_chapter("previous") is False
+    assert messages[-1] == "Already at first chapter"
+
+
+def test_save_current_position_writes_positive_values() -> None:
+    """Ensure save_current_position persists elapsed time via library client."""
+    calls: list[tuple[str, float]] = []
+    library = type(
+        "Library",
+        (),
+        {"save_last_position": lambda self, asin, pos: calls.append((asin, pos))},
+    )()
+    controller = PlaybackController(lambda _msg: None, library)
+    controller.current_asin = "ASIN"
+    controller.is_playing = True
+    controller.playback_start_time = 1.0
+    controller.seek_offset = 10.0
+    controller._get_current_elapsed = lambda: 15.0
+    controller._save_current_position()
+    assert calls == [("ASIN", 25.0)]
+
+
+def test_update_position_if_needed_honors_interval(monkeypatch) -> None:
+    """Ensure periodic save runs only when interval has elapsed."""
+    controller, _ = _controller()
+    controller.is_playing = True
+    controller.current_asin = "ASIN"
+    controller.library_client = object()
+    controller.last_save_time = 10.0
+    controller.position_save_interval = 30.0
+    saves: list[str] = []
+    monkeypatch.setattr(
+        controller, "_save_current_position", lambda: saves.append("save")
+    )
+    monkeypatch.setattr(seek_speed_mod.time, "time", lambda: 20.0)
+    controller.update_position_if_needed()
+    monkeypatch.setattr(seek_speed_mod.time, "time", lambda: 45.0)
+    controller.update_position_if_needed()
+    assert saves == ["save"]
+
+
+def test_change_speed_restarts_with_new_rate(monkeypatch) -> None:
+    """Ensure speed changes restart playback at current position."""
+    controller, _ = _controller()
+    controller.playback_speed = 1.0
+    controller.seek_offset = 5.0
+    monkeypatch.setattr(controller, "_get_current_elapsed", lambda: 10.0)
+    seen: list[tuple[float, float, str]] = []
+
+    def fake_restart(
+        position: float, speed: float | None = None, message: str | None = None
+    ) -> bool:
+        """Capture restart call parameters."""
+        seen.append((position, speed or 0.0, message or ""))
+        return True
+
+    monkeypatch.setattr(controller, "_restart_at_position", fake_restart)
+    assert controller.increase_speed() is True
+    assert seen and seen[0][0] == 15.0
+    assert seen[0][1] > 1.0
+    assert seen[0][2].startswith("Speed: ")
diff --git a/tests/playback/test_playback_controller_state_mixin.py b/tests/playback/test_playback_controller_state_mixin.py
new file mode 100644
index 0000000..d035364
--- /dev/null
+++ b/tests/playback/test_playback_controller_state_mixin.py
@@ -0,0 +1,76 @@
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Any, cast
+
+from auditui.playback import controller_state as state_mod
+from auditui.playback.controller import PlaybackController
+
+
+class Proc:
+    """Simple process shim exposing poll and pid for state tests."""
+
+    def __init__(self, poll_value=None) -> None:
+        """Store poll return value and fake pid."""
+        self._poll_value = poll_value
+        self.pid = 123
+
+    def poll(self):
+        """Return configured process status code or None."""
+        return self._poll_value
+
+
+def _controller() -> tuple[PlaybackController, list[str]]:
+    """Build playback controller and collected notifications list."""
+    messages: list[str] = []
+    return PlaybackController(messages.append, None), messages
+
+
+def test_get_current_elapsed_rolls_pause_into_duration(monkeypatch) -> None:
+    """Ensure elapsed helper absorbs stale pause_start_time when resumed."""
+    controller, _ = _controller()
+    controller.pause_start_time = 100.0
+    controller.is_paused = False
+    monkeypatch.setattr(state_mod.time, "time", lambda: 120.0)
+    monkeypatch.setattr(state_mod.elapsed_mod, "get_elapsed", lambda *args: 50.0)
+    assert controller._get_current_elapsed() == 50.0
+    assert controller.paused_duration == 20.0
+    assert controller.pause_start_time is None
+
+
+def test_validate_playback_state_stops_when_process_ended() -> None:
+    """Ensure state validation stops and reports when process is gone."""
+    controller, messages = _controller()
+    controller.playback_process = cast(Any, Proc(poll_value=1))
+    controller.is_playing = True
+    controller.current_file_path = Path("book.aax")
+    ok = controller._validate_playback_state(require_paused=False)
+    assert ok is False
+    assert messages[-1] == "Playback process has ended"
+
+
+def test_send_signal_sets_paused_state_and_notifies(monkeypatch) -> None:
+    """Ensure SIGSTOP updates paused state and includes filename in status."""
+    controller, messages = _controller()
+    controller.playback_process = cast(Any, Proc())
+    controller.current_file_path = Path("book.aax")
+    monkeypatch.setattr(state_mod.process_mod, "send_signal", lambda proc, sig: None)
+    controller._send_signal(state_mod.signal.SIGSTOP, "Paused", "pause")
+    assert controller.is_paused is True
+    assert messages[-1] == "Paused: book.aax"
+
+
+def test_send_signal_handles_process_lookup(monkeypatch) -> None:
+    """Ensure missing process lookup errors are handled with user-facing message."""
+    controller, messages = _controller()
+    controller.playback_process = cast(Any, Proc())
+
+    def raise_lookup(proc, sig):
+        """Raise process lookup error to exercise exception path."""
+        del proc, sig
+        raise ProcessLookupError("gone")
+
+    monkeypatch.setattr(state_mod.process_mod, "send_signal", raise_lookup)
+    monkeypatch.setattr(state_mod.process_mod, "terminate_process", lambda proc: None)
+    controller._send_signal(state_mod.signal.SIGCONT, "Playing", "resume")
+    assert messages[-1] == "Process no longer exists"