transfer: add test

bit hard to test the 1.2 -> 2.0 transfer, but we can at least
test the 2.0 -> 2.0 "NoOp" transfer.

src/borg/testsuite/archiver.py

@@ -3765,6 +3765,32 @@ id: 2 / e29442 3506da 4e1ea7 / 25f62a 5a3d41 - 02
             key = msgpack.unpackb(a2b_base64(repository.load_key()))
             assert key["algorithm"] == "argon2 chacha20-poly1305"
 
+    def test_transfer(self):
+        def check_repo(repo_option):
+            listing = self.cmd(repo_option, "rlist", "--short")
+            assert "arch1" in listing
+            assert "arch2" in listing
+            listing = self.cmd(repo_option, "list", "--short", "arch1")
+            assert "file1" in listing
+            assert "dir2/file2" in listing
+            self.cmd(repo_option, "check")
+
+        self.create_test_files()
+        repo1 = f"--repo={self.repository_location}1"
+        repo2 = f"--repo={self.repository_location}2"
+        other_repo1 = f"--other-repo={self.repository_location}1"
+
+        self.cmd(repo1, "rcreate", RK_ENCRYPTION)
+        self.cmd(repo1, "create", "arch1", "input")
+        self.cmd(repo1, "create", "arch2", "input")
+        check_repo(repo1)
+
+        self.cmd(repo2, "rcreate", RK_ENCRYPTION, other_repo1)
+        self.cmd(repo2, "transfer", other_repo1, "--dry-run")
+        self.cmd(repo2, "transfer", other_repo1)
+        self.cmd(repo2, "transfer", other_repo1, "--dry-run")
+        check_repo(repo2)
+
 
 @unittest.skipUnless("binary" in BORG_EXES, "no borg.exe available")
 class ArchiverTestCaseBinary(ArchiverTestCase):