FileSnapshotTest: Add more MISSING_FILE coverage

Add a couple tests that confirm what the docs say about isModified() and
equals(MISSING_FILE) behavior.

Change-Id: I6093040ba3594934c3270331405a44b2634b97c5
Signed-off-by: Nasser Grainawi <quic_nasserg@quicinc.com>
diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/FileSnapshotTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/FileSnapshotTest.java
index 5e87b8f..12773c2 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/FileSnapshotTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/FileSnapshotTest.java
@@ -209,6 +209,20 @@ public void fileSnapshotEquals() throws Exception {
 		assertTrue(fs2.equals(fs1));
 	}
 
+	@Test
+	public void snapshotAndFileMissingIsNotModified() throws Exception {
+		File doesNotExist = trash.resolve("DOES_NOT_EXIST").toFile();
+		FileSnapshot missing = FileSnapshot.save(doesNotExist);
+		assertFalse(missing.isModified(doesNotExist));
+	}
+
+	@Test
+	public void missingFileEquals() throws Exception {
+		FileSnapshot missing = FileSnapshot.save(
+				trash.resolve("DOES_NOT_EXIST").toFile());
+		assertTrue(missing.equals(FileSnapshot.MISSING_FILE));
+	}
+
 	@SuppressWarnings("boxing")
 	@Test
 	public void detectFileModified() throws IOException {