run-tests: add 'vm' command

examples/README.md

@@ -45,9 +45,14 @@ the host system.
 git clone https://github.com/fort-nix/nix-bitcoin
 cd nix-bitcoin/test
 
+# Run a node in a VM. No tests are executed.
+./run-tests.sh vm
+systemctl status bitcoind
+
 # Run a Python test shell inside a VM node
 ./run-tests.sh debug
 print(succeed("systemctl status bitcoind"))
+run_test("bitcoind")
 
 # Run a node in a container. Requires systemd and root privileges.
 ./run-tests.sh container

test/lib/make-test.nix

@@ -61,5 +61,23 @@ name: testConfig:
     };
   };
 
+  # This allows running a test scenario in a regular NixOS VM.
+  # No tests are executed.
+  vmWithoutTests = (pkgs.nixos {
+    imports = [
+      testConfig
+      "${toString pkgs.path}/nixos/modules/virtualisation/qemu-vm.nix"
+    ];
+    virtualisation.graphics = false;
+    services.mingetty.autologinUser = "root";
+
+    # Provide a shortcut for instant poweroff from within the machine
+    environment.systemPackages = with pkgs; [
+      (lowPrio (writeScriptBin "q" ''
+         echo o >/proc/sysrq-trigger
+       ''))
+    ];
+  }).vm;
+
   config = testConfig;
 }

test/run-tests.sh

@@ -42,6 +42,14 @@
 #     For now, creating NixOS containers requires root permissions.
 #     See ./lib/make-container.sh for a complete documentation.
 #
+#   Run a test scenario in a regular NixOS VM.
+#   No tests are executed, the machine's serial console is attached to your terminal.
+#   ./run-tests.sh [--scenario <scenario>] vm
+#
+#     This is useful for directly exploring a test configuration without the
+#     intermediate Python REPL layer.
+#     Run command 'q' inside the machine for instant poweroff.
+#
 #   Run tests from a snapshot copy of the source files
 #   ./run-tests.sh --copy-src|-c ...
 #
@@ -170,6 +178,24 @@ container() {
     "$scriptDir/lib/make-container.sh" "$@"
 }
 
+# Run a regular NixOS VM
+vm() {
+    export TMPDIR=$(mktemp -d /tmp/nix-bitcoin-vm.XXX)
+    runAtExit+="rm -rf $TMPDIR;"
+
+    nix-build --out-link $TMPDIR/vm -E "((import \"$scriptDir/tests.nix\" {}).getTest \"$scenario\").vmWithoutTests"
+
+    echo "VM stats: CPUs: $numCPUs, memory: $memoryMiB MiB"
+    extraNetOpts=
+    [[ $NB_TEST_ENABLE_NETWORK ]] || extraNetOpts='restrict=on'
+
+    USE_TMPDIR=1 \
+    NIX_DISK_IMAGE=$TMPDIR/img.qcow2 \
+    QEMU_OPTS="-smp $numCPUs -m $memoryMiB -nographic $QEMU_OPTS"  \
+    QEMU_NET_OPTS="$extraNetOpts $QEMU_NET_OPTS" \
+      $TMPDIR/vm/bin/run-*-vm
+}
+
 doBuild() {
     name=$1
     shift