From db5b1678a3970b1eacd669b8e0f634d88386b2fa Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Fri, 13 Nov 2026 21:35:09 +0000
Subject: tests: run scenarios selected by name

nix-build tests -A only --argstr only REGEX runs the scenarios whose
names match the regular expression REGEX in a single VM test, like the
smoke test, e.g. --argstr only 'lock-hooks-.*' for lock-hooks on all
three kinds of targets.
---
 README.md         |  1 +
 tests/default.nix | 27 +++++++++++++++++++++++----
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 8b0a5d0..a93c0f6 100644
--- a/README.md
+++ b/README.md
@@ -765,6 +765,7 @@ nix-build tests -A exhaustive     # all exhaustive tests
 nix-build tests -A exhaustive.git # the remaining combinations of one test
 nix-build tests -A rsync-3-5-0    # the scenarios depending on rsync's version
 nix-build tests -A smoke          # a few scenarios of each kind, in one VM
+nix-build tests -A only --argstr only 'lock-hooks-.*'  # scenarios by name
 ```
 
 Populate is a program in Rust, in `pkgs/populate`, which
diff --git a/tests/default.nix b/tests/default.nix
index 97b64e0..0e59e26 100644
--- a/tests/default.nix
+++ b/tests/default.nix
@@ -7,8 +7,10 @@
 # -A exhaustive, or one with, e.g., nix-build tests -A exhaustive.flake.
 # The smoke test runs a few scenarios covering each source type and each kind
 # of target in a single VM test, for checking changes quickly; build it with
-# nix-build tests -A smoke.
-{ pkgs ? import ../pkgs {} }:
+# nix-build tests -A smoke.  nix-build tests -A only --argstr only REGEX runs
+# the scenarios whose names match the regular expression REGEX in a single
+# VM test, e.g. --argstr only 'lock-hooks-.*'.
+{ pkgs ? import ../pkgs {}, only ? null }:
 
 let
   # HEAD of /fixtures/gitsrc, which fixtures.sh creates deterministically,
@@ -72,15 +74,27 @@ let
     "deploy-local-buildTarget0-etcFlake0-flakefile"
     "deploy-sudo-allocateTTY"
   ];
+  allScenarios = pkgs.lib.concatLists (builtins.attrValues scenarios);
   smokeScenarios = let
-    all = pkgs.lib.concatLists (builtins.attrValues scenarios);
-    selected = builtins.filter (scenario: builtins.elem scenario.name smokeNames) all;
+    selected = builtins.filter (scenario: builtins.elem scenario.name smokeNames) allScenarios;
     missing = pkgs.lib.subtractLists (map (scenario: scenario.name) selected) smokeNames;
   in
     if missing != [] then
       throw "tests: smoke test names missing scenarios: ${toString missing}"
     else
       selected;
+  # The scenarios whose names match the regular expression only.
+  onlyScenarios = let
+    selected = builtins.filter
+      (scenario: builtins.match only scenario.name != null)
+      allScenarios;
+  in
+    if only == null then
+      throw "tests: -A only needs --argstr only REGEX"
+    else if selected == [] then
+      throw "tests: no scenario's name matches ${builtins.toJSON only}"
+    else
+      selected;
 in
   testsOf false ""
   # Not built by nix-build tests either, which runs these scenarios anyway.
@@ -90,6 +104,11 @@ in
       name = "smoke";
       scenarios = smokeScenarios;
     };
+    only.only = import ./vm.nix {
+      inherit pkgs gitHead;
+      name = "only";
+      scenarios = onlyScenarios;
+    };
   }
   # An attribute set without recurseForDerivations, so nix-build tests
   # doesn't build them.
-- 
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