python3Packages.beets: add single-plugin passthru tests

Add a positive `beet --help` check for every functional built-in plugin,
with only that plugin enabled.

Assisted-by: Codex (GPT-5)
Co-Authored-By: Doron Behar <doron.behar@gmail.com>

pkgs/development/python-modules/beets/default.nix

@@ -278,7 +278,9 @@ buildPythonPackage (finalAttrs: {
         bench.testPaths = [ ];
         bpd = { };
         bpm.testPaths = [ ];
-        bpsync.testPaths = [ ];
+        bpsync = {
+          testPaths = [ ];
+        };
         bucket = { };
         chroma = {
           propagatedBuildInputs = [ pyacoustid ];
@@ -291,10 +293,15 @@ buildPythonPackage (finalAttrs: {
           propagatedBuildInputs = [ requests ];
           testPaths = [ ];
         };
-        discogs.propagatedBuildInputs = [
-          discogs-client
-          requests
-        ];
+        discogs = {
+          propagatedBuildInputs = [
+            discogs-client
+            requests
+          ];
+          singlePluginTest.config = {
+            user_token = "test";
+          };
+        };
         duplicates.testPaths = [ ];
         edit = { };
         embedart = {
@@ -337,7 +344,10 @@ buildPythonPackage (finalAttrs: {
           testPaths = [ ];
         };
         limit = { };
-        listenbrainz = { };
+        listenbrainz.singlePluginTest.config = {
+          token = "test";
+          username = "test";
+        };
         loadext = {
           propagatedBuildInputs = [ requests ];
           testPaths = [ ];
@@ -366,11 +376,14 @@ buildPythonPackage (finalAttrs: {
         plexupdate = { };
         random = { };
         replace = { };
-        replaygain.wrapperBins = [
-          aacgain
-          ffmpeg
-          mp3gain
-        ];
+        replaygain = {
+          singlePluginTest.config.backend = "gstreamer";
+          wrapperBins = [
+            aacgain
+            ffmpeg
+            mp3gain
+          ];
+        };
         rewrite.testPaths = [ ];
         scrub.testPaths = [ ];
         smartplaylist = { };
@@ -378,7 +391,10 @@ buildPythonPackage (finalAttrs: {
           propagatedBuildInputs = [ soco ];
           testPaths = [ ];
         };
-        spotify = { };
+        spotify.singlePluginTest.setup = ''
+          mkdir -p $HOME/.config/beets
+          echo '{"access_token":"test"}' > $HOME/.config/beets/spotify_token.json
+        '';
         subsonicplaylist = {
           propagatedBuildInputs = [ requests ];
           testPaths = [ ];
@@ -428,6 +444,10 @@ buildPythonPackage (finalAttrs: {
             enable = !disableAllPlugins;
             builtin = false;
             propagatedBuildInputs = [ ];
+            singlePluginTest = {
+              config = { };
+              setup = "";
+            };
             testPaths = [ "test/plugins/test_${n}.py" ];
             wrapperBins = [ ];
           } a
@@ -497,7 +517,66 @@ buildPythonPackage (finalAttrs: {
           -c $out/config.yaml \
           mpdstats --help 2> $out/mpdstats-help-stderr || true
       '';
-    };
+    }
+    # Build and start beets once for each supported built-in plugin. Keeping the
+    # plugins isolated makes missing optional dependencies visible.
+    // lib.pipe finalAttrs.finalPackage.passthru.plugins.all [
+      # Deprecated plugins are not useful regression targets.
+      (lib.filterAttrs (_: pluginAttrs: !(pluginAttrs.deprecated or false)))
+      (lib.concatMapAttrs (
+        pluginName: pluginAttrs:
+        let
+          testConfig = {
+            plugins = [ pluginName ];
+          }
+          # Some plugins do not accept an empty attribute set as config.
+          // lib.optionalAttrs (pluginAttrs.singlePluginTest.config != { }) {
+            ${pluginName} = pluginAttrs.singlePluginTest.config;
+          };
+          beetsWithSinglePlugin = beets.override {
+            disableAllPlugins = true;
+            pluginOverrides = {
+              ${pluginName}.enable = true;
+            };
+            # The runCommand below is the relevant check; avoid running
+            # the full upstream test suite once per plugin. NOTE that
+            # testing whether any plugin's `testPaths` is incorrect, is
+            # done for all plugins via the `beets-minimal` derivation.
+            doCheck = false;
+          };
+        in
+        {
+          "with-single-plugin-${pluginName}" = beetsWithSinglePlugin;
+          "single-plugin-${pluginName}" = runCommand "beets-single-plugin-${pluginName}-test" { } ''
+            set -euo pipefail
+            export HOME=$(mktemp -d)
+            ${pluginAttrs.singlePluginTest.setup}
+            mkdir $out
+
+            cat <<'EOF' > $out/config.yaml
+            ${lib.generators.toYAML { } testConfig}
+            EOF
+
+            status=0
+            ${lib.getExe beetsWithSinglePlugin} \
+              -c "$out/config.yaml" \
+              --help > "$out/stdout" 2> "$out/stderr" || status=$?
+
+            # beet exits successfully when a plugin fails to load, so its
+            # stderr must also be checked for the diagnostic.
+            if (( status != 0 )) || grep -Fq "error loading plugin" "$out/stderr"; then
+              {
+                printf '%s\n' '----- stdout -----'
+                cat "$out/stdout"
+                printf '%s\n' '----- stderr -----'
+                cat "$out/stderr"
+              } >&2
+              exit 1
+            fi
+          '';
+        }
+      ))
+    ];
   };
 
   meta = {