check that at least one test was added

t/merge-ready/added-test.t

@@ -0,0 +1,35 @@
+use 5.38.0;
+
+use Test2::V0;
+
+use Git::Wrapper;
+
+my $target_branch = $ENV{TARGET_BRANCH} // 'main';
+
+my $git = Git::Wrapper->new('.');
+
+my $on_target = grep { "* $target_branch" eq $_ } $git->branch;
+
+if ($on_target) {
+    pass "nothing to check here";
+}
+else {
+    my @diff = $git->diff($target_branch);
+    ok test_file_modified(@diff), "added to a test file";
+}
+
+sub test_file_modified (@diff) {
+    my $in_test_file = 0;
+    for (@diff) {
+        if (/^diff/) {
+            $in_test_file = /\.t$/;
+            next;
+        }
+
+        return 1 if $in_test_file and /^\+/;
+    }
+
+    return 0;
+}
+
+done_testing;