diff --git a/find_bad_motion_tracks/find_bad_tracks.py b/find_bad_motion_tracks/find_bad_tracks.py
index 482ae20..a201665 100644
--- a/find_bad_motion_tracks/find_bad_tracks.py
+++ b/find_bad_motion_tracks/find_bad_tracks.py
@@ -163,7 +163,7 @@ def combine_badnesses(*args: Dict[str, Badness]) -> Dict[str, Badness]:
             adjusted_amount = badness.amount
             if percentile != 0:
                 adjusted_amount = badness.amount / percentile
-            if adjusted_amount > to_beat_amount:
+            if adjusted_amount > to_beat_amount or track not in combined:
                 combined[track] = Badness(adjusted_amount, badness.frame)
 
     return combined
@@ -183,7 +183,7 @@ def find_bad_tracks(clip: MovieClip) -> Dict[str, Badness]:
     # Map track names to marker shape change amounts
     shape_badnesses: Dict[str, Badness] = {}
 
-    for frame_index in range(first_frame_index + 1, last_frame_index):
+    for frame_index in range(first_frame_index + 1, last_frame_index + 1):
         dx_list: List[TrackWithFloat] = []
         dy_list: List[TrackWithFloat] = []
         ddx_list: List[TrackWithFloat] = []
diff --git a/tests/test_find_bad_tracks.py b/tests/test_find_bad_tracks.py
index a6ac15c..75eb693 100644
--- a/tests/test_find_bad_tracks.py
+++ b/tests/test_find_bad_tracks.py
@@ -1,35 +1,80 @@
-from typing import cast, List
+from typing import cast, List, Tuple, Optional, Union, Any
 
 from bpy.types import (
     MovieClip,
     MovieTracking,
     MovieTrackingTrack,
     MovieTrackingTracks,
+    MovieTrackingMarkers,
     MovieTrackingMarker,
 )
 
 from find_bad_motion_tracks.find_bad_tracks import (
     find_bad_tracks,
     shape_change_amount,
+    Badness,
     BadnessCalculator,
     TrackWithFloat,
 )
 
 
+class TestMovieTrackingMarkers(MovieTrackingMarkers):
+    def __init__(self, coordinates: List[Tuple[float, float]]) -> None:
+        super().__init__()
+
+        self.coordinates = coordinates
+
+    def find_frame(
+        self, frame: Optional[int], exact: Optional[Union[bool, Any]] = True
+    ) -> "MovieTrackingMarker":
+        marker = MovieTrackingMarker()
+        if frame is None or frame < 0 or frame >= len(self.coordinates):
+            marker.mute = True
+            return marker
+
+        marker.co = self.coordinates[frame]
+
+        # Badness code expects markers to come with four corners. Corners are
+        # relative to the marker position, so we give all markers the same
+        # corners.
+        marker.pattern_corners = [[-1.0, -1.0], [-1.0, 1.0], [1.0, 1.0], [1.0, -1.0]]
+        return marker
+
+
 def make_clip() -> MovieClip:
-    tracks: List[MovieTrackingTrack] = []
+    """
+    Create a clip with two frames and four tracks, each track moving 10 to the right.
+
+    Each track is a list of x-y coordinate tuples.
+
+    Each x-y coordinate tuple represents the marker position at one frame.
+    """
+    movieTrackingTracks: List[MovieTrackingTrack] = []
+    for i in range(4):
+        movieTrackingTrack = MovieTrackingTrack()
+        movieTrackingTrack.name = f"Track {i}"
+
+        y = i * 10.0 + 10.0
+        track = [(0.0 + y * 20.0, y), (10.0 + y * 20.0, y)]
+        movieTrackingTrack.markers = TestMovieTrackingMarkers(track)
+
+        movieTrackingTracks.append(movieTrackingTrack)
 
     clip = MovieClip()
     clip.frame_start = 0
-    clip.frame_duration = 10
+    clip.frame_duration = 2
     clip.tracking = MovieTracking()
-    clip.tracking.tracks = cast(MovieTrackingTracks, tracks)
+    clip.tracking.tracks = cast(MovieTrackingTracks, movieTrackingTracks)
     return clip
 
 
-def test_find_bad_tracks_no_tracks() -> None:
-    test_clip = make_clip()
-    find_bad_tracks(test_clip)
+def test_find_bad_tracks_all_good() -> None:
+    assert find_bad_tracks(make_clip()) == {
+        "Track 0": Badness(0.0, 1),
+        "Track 1": Badness(0.0, 1),
+        "Track 2": Badness(0.0, 1),
+        "Track 3": Badness(0.0, 1),
+    }
 
 
 def test_compute_badness_score() -> None: