Complete scheduler state transition tests

docs/input-folder-scheduler-plan.md

@@ -28,7 +28,7 @@ Note: the local machine's filesystem root is read-only in this workspace, so abs
 8. [x] Add FFmpeg clipping into `/output/clips/<video-name>/` using 8-second MP4/H.264/AAC segments.
 9. [x] Add success handling that moves processed source files to processed storage.
 10. [x] Add failure handling for FFmpeg or filesystem errors.
-11. [ ] Add unit tests for ordering, invalid-file handling, repeat prevention, and state transitions.
+11. [x] Add unit tests for ordering, invalid-file handling, repeat prevention, and state transitions.
 12. [ ] Add optional FFmpeg integration test for a short fixture.
 13. [ ] Add local profile or documented runtime config for enabling the scheduler.
 14. [ ] Run verification and mark feature complete.

src/test/java/org/example/videoclips/folder/FolderVideoScanSchedulerTest.java

@@ -10,6 +10,8 @@ import java.nio.file.Path;
 import java.nio.file.attribute.PosixFilePermission;
 import java.util.Optional;
 import java.util.Set;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -122,6 +124,31 @@ class FolderVideoScanSchedulerTest {
         assertEquals("video", Files.readString(tempDir.resolve("processed/1.mp4")));
     }
 
+    @Test
+    void processesOneCandidatePerScanInNaturalOrder() throws Exception {
+        Files.writeString(tempDir.resolve("2.mp4"), "second");
+        Files.writeString(tempDir.resolve("1.mp4"), "first");
+        List<String> clippedSources = new ArrayList<>();
+        FolderFfmpegClipper clipper = mock(FolderFfmpegClipper.class);
+        when(clipper.clip(any())).thenAnswer(invocation -> {
+            Path source = invocation.getArgument(0);
+            clippedSources.add(source.getFileName().toString());
+            return new FolderFfmpegClipper.ClipResult(tempDir.resolve("output/result"), 1);
+        });
+        FolderVideoScanScheduler scheduler = scheduler(tempDir, acceptedValidator(), clipper);
+
+        scheduler.scan();
+
+        assertEquals(List.of("1.mp4"), clippedSources);
+        assertTrue(Files.exists(tempDir.resolve("processed/1.mp4")));
+        assertTrue(Files.exists(tempDir.resolve("2.mp4")));
+
+        scheduler.scan();
+
+        assertEquals(List.of("1.mp4", "2.mp4"), clippedSources);
+        assertTrue(Files.exists(tempDir.resolve("processed/2.mp4")));
+    }
+
     @Test
     void invalidCandidateIsMovedToRejectedDirectory() throws Exception {
         Files.writeString(tempDir.resolve("invalid.mp4"), "not video");