chore: Make signing tests more robust

Old tests didn't verify the signatures were produced and also assumed
that signing config wasn't set up wherever you ran tests. Since I do
use signed commits now for my own work, this was a bad assumption and
made the tests fail locally.

Now we check for either the signature to be present or that signing
failed because no secret key was found.

For disabling signing, we ensure that no signature was added to the commit.

src/compatTest/groovy/org/ajoberstar/gradle/git/publish/BaseCompatTest.groovy

@@ -8,6 +8,8 @@ import org.gradle.testkit.runner.UnexpectedBuildFailure
 import spock.lang.Specification
 import spock.lang.TempDir
 
+import java.rmi.UnexpectedException
+
 class BaseCompatTest extends Specification {
   @TempDir File tempDir
   File projectDir
@@ -420,10 +422,15 @@ gitPublish {
 }
 """
     when:
-    def result = buildAndFail()
+    def result = buildOrFail()
 
     then:
-    result.output.contains("gpg: signing failed: No secret key")
+    def newCommit = remote.resolve.toCommit("gh-pages").id
+    def remoteGitDir = "${remote.repository.rootDir}/.git"
+    def proc = "git --git-dir ${remoteGitDir} cat-file -p ${newCommit}".execute()
+    def latestCommit = proc.in.text
+    // either it will work and sign or the key will be missing and it won't be able to
+    latestCommit.contains("gpgsig") || result.output.contains("gpg: signing failed: No secret key")
   }
 
   def 'can deactivate signing'() {
@@ -451,6 +458,12 @@ gitPublish {
 
     then:
     result.task(':gitPublishPush').outcome == TaskOutcome.SUCCESS
+
+    def newCommit = remote.resolve.toCommit("gh-pages").id
+    def remoteGitDir = "${remote.repository.rootDir}/.git"
+    def proc = "git --git-dir ${remoteGitDir} cat-file -p ${newCommit}".execute()
+    def latestCommit = proc.in.text
+    !latestCommit.contains('gpgsign')
   }
 
   private BuildResult build(String... args = ['gitPublishPush', '--stacktrace', '--configuration-cache']) {
@@ -461,6 +474,14 @@ gitPublish {
     return runner(args).buildAndFail()
   }
 
+  private BuildResult buildOrFail(String... args = ['gitPublishPush', '--stacktrace', '--configuration-cache']) {
+    try {
+      return runner(args).build()
+    } catch (UnexpectedBuildFailure e) {
+      return e.buildResult
+    }
+  }
+
   private GradleRunner runner(String... args) {
     return GradleRunner.create()
       .withGradleVersion(System.properties['compat.gradle.version'])