test: add tests for the new behavior in the rebase engine

Author: slarse

crates/but-rebase/tests/fixtures/generated-archives/.gitignore

@@ -1,4 +1,5 @@
 /*.tar
 !four-commits-signed.tar
 !workspace-signed.tar
-!workspace-with-wc-content-signed.tar
+!workspace-with-wc-content-signed.tar
+!unsigned-commits-with-signing-key-setup-but-signing-disabled.tar

crates/but-rebase/tests/fixtures/generated-archives/unsigned-commits-with-signing-key-setup-but-signing-disabled.tar

@@ -0,0 +1,23 @@
+#!/bin/bash
+#
+# Description: Scenario with unsigned commits and commit signing disabled, but
+# all the requisite configuration to sign commits is present.
+#
+# The scenario is designed to be used to test signing of commits in the absence
+# of other changes.
+
+set -eu -o pipefail
+
+git init
+
+ssh-keygen -t rsa -b 2048 -C "test@example.com" -N "" -f signature.key
+git config gpg.format ssh
+git config user.signingKey "$PWD/signature.key"
+echo "*.key*" >.gitignore
+
+echo "base" >base && git add . && git commit -m "base"
+git update-ref refs/heads/base $(git rev-parse HEAD)
+echo "mid" >mid && git add . && git commit -m "mid"
+git update-ref refs/heads/mid $(git rev-parse HEAD)
+echo "top" >top && git add . && git commit -m "top"
+git update-ref refs/heads/top $(git rev-parse HEAD)