test: improve modularization

This improves debugging and experimenting by making it easy to compose fine-grained
scenarios that have specific tests and features enabled.

The VM test output now includes the subtest name and duration.

Remove the 'raise Exception()' hack for interactive mode.

Run 'banlist-and-restart' test before 'backups'. This speeds up the test
by avoiding an extra shutdown of all bitcoin-related services.

test/lib/make-test.nix

@@ -0,0 +1,41 @@
+scenario: testConfig:
+
+{
+  vm = import ./make-test-vm.nix {
+    name = "nix-bitcoin-${scenario}";
+
+    machine = {
+      imports = [ testConfig ];
+      # Needed because duplicity requires 270 MB of free temp space, regardless of backup size
+      virtualisation.diskSize = 1024;
+    };
+
+    testScript = nodes: let
+      cfg = nodes.nodes.machine.config;
+      data = {
+        data = cfg.test.data;
+        tests = cfg.tests;
+      };
+      dataFile = builtins.toFile "test-data" (builtins.toJSON data);
+      initData = ''
+        import json
+
+        with open("${dataFile}") as f:
+            data = json.load(f)
+
+        enabled_tests = set(test for (test, enabled) in data["tests"].items() if enabled)
+        test_data = data["data"]
+      '';
+    in
+      builtins.concatStringsSep "\n\n" [
+        initData
+        (builtins.readFile ./../tests.py)
+        # Don't run tests in interactive mode.
+        # is_interactive is set in ../run-tests.sh
+        ''
+          if not "is_interactive" in vars():
+              run_tests()
+        ''
+      ];
+  };
+}