Add a test where only one hunk in a file is dropped

test/mechanicaldiff.bats

@@ -29,3 +29,67 @@ setup() {
   assert_failure
   assert_output ""
 }
+
+@test "drops one hunk and keeps another" {
+  cat >"$BATS_TEST_TMPDIR/old" <<-'EOF'
+	alpha
+	beta
+	gamma
+	one
+	two
+	three
+	four
+	five
+	six
+	seven
+	eight
+	nine
+	ten
+	delta
+	EOF
+  cat >"$BATS_TEST_TMPDIR/new" <<-'EOF'
+	alpha
+	beta_changed
+	gamma
+	one
+	two
+	three
+	four
+	five
+	six
+	seven
+	eight
+	nine
+	ten
+	delta_changed
+	EOF
+  cat >"$BATS_TEST_TMPDIR/new_kept" <<-'EOF'
+	alpha
+	beta_changed
+	gamma
+	one
+	two
+	three
+	four
+	five
+	six
+	seven
+	eight
+	nine
+	ten
+	delta
+	EOF
+
+  git diff --no-index "$BATS_TEST_TMPDIR/old" \
+    "$BATS_TEST_TMPDIR/new" \
+    >"$BATS_TEST_TMPDIR/diff_full" || true
+  git diff --no-index "$BATS_TEST_TMPDIR/old" \
+    "$BATS_TEST_TMPDIR/new_kept" \
+    >"$BATS_TEST_TMPDIR/diff_expected" || true
+
+  run mechanicaldiff.py "beta" "beta_changed" <"$BATS_TEST_TMPDIR/diff_full"
+  assert_failure
+  assert_output --partial "-beta"
+  assert_output --partial "+beta_changed"
+  refute_output --partial "delta_changed"
+}