diff --git a/pkgs/build-support/trivial-builders/test/default.nix b/pkgs/build-support/trivial-builders/test/default.nix
index 59dbba3f1841..f41372d922bb 100644
--- a/pkgs/build-support/trivial-builders/test/default.nix
+++ b/pkgs/build-support/trivial-builders/test/default.nix
@@ -26,6 +26,9 @@ recurseIntoAttrs {
     then references
     else {};
   writeCBin = callPackage ./writeCBin.nix {};
+  writeClosure-union = callPackage ./writeClosure-union.nix {
+    inherit (references) samples;
+  };
   writeShellApplication = callPackage ./writeShellApplication.nix {};
   writeScriptBin = callPackage ./writeScriptBin.nix {};
   writeShellScript = callPackage ./write-shell-script.nix {};
diff --git a/pkgs/build-support/trivial-builders/test/references/default.nix b/pkgs/build-support/trivial-builders/test/references/default.nix
index 3e21c905321e..928cc1d9461f 100644
--- a/pkgs/build-support/trivial-builders/test/references/default.nix
+++ b/pkgs/build-support/trivial-builders/test/references/default.nix
@@ -12,7 +12,7 @@
 , cleanSamples ? lib.filterAttrs (n: lib.isStringLike)
   # Test targets
 , writeDirectReferencesToFile
-, writeReferencesToFile
+, writeClosure
 }:
 
 # -------------------------------------------------------------------------- #
@@ -46,8 +46,9 @@ let
   samplesToString = attrs:
     lib.concatMapStringsSep " " (name: "[${name}]=${lib.escapeShellArg "${attrs.${name}}"}") (builtins.attrNames attrs);
 
-  references = lib.mapAttrs (n: v: writeReferencesToFile v) samples;
+  closures = lib.mapAttrs (n: v: writeClosure [ v ]) samples;
   directReferences = lib.mapAttrs (n: v: writeDirectReferencesToFile v) samples;
+  collectiveClosure = writeClosure (lib.attrValues samples);
 
   testScriptBin = stdenvNoCC.mkDerivation (finalAttrs: {
     name = "references-test";
@@ -61,8 +62,9 @@ let
       mkdir -p "$out/bin"
       substitute "$src" "$out/bin/${finalAttrs.meta.mainProgram}" \
         --replace "@SAMPLES@" ${lib.escapeShellArg (samplesToString samples)} \
-        --replace "@REFERENCES@" ${lib.escapeShellArg (samplesToString references)} \
-        --replace "@DIRECT_REFS@" ${lib.escapeShellArg (samplesToString directReferences)}
+        --replace "@CLOSURES@" ${lib.escapeShellArg (samplesToString closures)} \
+        --replace "@DIRECT_REFS@" ${lib.escapeShellArg (samplesToString directReferences)} \
+        --replace "@COLLECTIVE_CLOSURE@" ${lib.escapeShellArg collectiveClosure}
       runHook postInstall
       chmod +x "$out/bin/${finalAttrs.meta.mainProgram}"
     '';
@@ -79,8 +81,9 @@ let
 
     passthru = {
       inherit
+        collectiveClosure
         directReferences
-        references
+        closures
         samples
         ;
     };
@@ -109,8 +112,9 @@ testers.nixosTest {
     '';
   passthru = {
     inherit
+      collectiveClosure
       directReferences
-      references
+      closures
       samples
       testScriptBin
       ;
diff --git a/pkgs/build-support/trivial-builders/test/references/references-test.sh b/pkgs/build-support/trivial-builders/test/references/references-test.sh
index 1b8f8e1504ec..92e4467287ed 100755
--- a/pkgs/build-support/trivial-builders/test/references/references-test.sh
+++ b/pkgs/build-support/trivial-builders/test/references/references-test.sh
@@ -33,16 +33,17 @@ set -euo pipefail
 
 cd "$(dirname "${BASH_SOURCE[0]}")"  # nixpkgs root
 
-  # Injected by Nix (to avoid evaluating in a derivation)
-  # turn them into arrays
-  # shellcheck disable=SC2206 # deliberately unquoted
-  declare -A samples=( @SAMPLES@ )
-  # shellcheck disable=SC2206 # deliberately unquoted
-  declare -A directRefs=( @DIRECT_REFS@ )
-  # shellcheck disable=SC2206 # deliberately unquoted
-  declare -A references=( @REFERENCES@ )
+  # Inject the path to compare from the Nix expression
 
-echo >&2 Testing direct references...
+  # Associative Arrays
+  declare -A samples=( @SAMPLES@ )
+  declare -A directRefs=( @DIRECT_REFS@ )
+  declare -A closures=( @CLOSURES@ )
+
+  # Path string
+  collectiveClosure=@COLLECTIVE_CLOSURE@
+
+echo >&2 Testing direct closures...
 for i in "${!samples[@]}"; do
   echo >&2 Checking "$i" "${samples[$i]}" "${directRefs[$i]}"
   diff -U3 \
@@ -52,10 +53,16 @@ done
 
 echo >&2 Testing closure...
 for i in "${!samples[@]}"; do
-  echo >&2 Checking "$i" "${samples[$i]}" "${references[$i]}"
+  echo >&2 Checking "$i" "${samples[$i]}" "${closures[$i]}"
   diff -U3 \
-    <(sort <"${references[$i]}") \
+    <(sort <"${closures[$i]}") \
     <(nix-store -q --requisites "${samples[$i]}" | sort)
 done
 
+echo >&2 Testing mixed closures...
+echo >&2 Checking all samples "(${samples[*]})" "$collectiveClosure"
+diff -U3 \
+  <(sort <"$collectiveClosure") \
+  <(nix-store -q --requisites "${samples[@]}" | sort)
+
 echo 'OK!'
diff --git a/pkgs/build-support/trivial-builders/test/writeClosure-union.nix b/pkgs/build-support/trivial-builders/test/writeClosure-union.nix
new file mode 100644
index 000000000000..92a2bf9f0988
--- /dev/null
+++ b/pkgs/build-support/trivial-builders/test/writeClosure-union.nix
@@ -0,0 +1,23 @@
+{ lib
+, runCommandLocal
+  # Test targets
+, writeClosure
+, samples
+}:
+runCommandLocal "test-trivial-builders-writeClosure-union" {
+  __structuredAttrs = true;
+  closures = lib.mapAttrs (n: v: writeClosure [ v ]) samples;
+  collectiveClosure = writeClosure (lib.attrValues samples);
+  inherit samples;
+  meta.maintainers = with lib.maintainers; [
+    ShamrockLee
+  ];
+} ''
+  set -eu -o pipefail
+  echo >&2 Testing mixed closures...
+  echo >&2 Checking all samples "(''${samples[*]})" "$collectiveClosure"
+  diff -U3 \
+    <(sort <"$collectiveClosure") \
+    <(cat "''${closures[@]}" | sort | uniq)
+  touch "$out"
+''
diff --git a/pkgs/build-support/trivial-builders/test/writeReferenceClosureToFile-mixed.nix b/pkgs/build-support/trivial-builders/test/writeReferenceClosureToFile-mixed.nix
deleted file mode 100644
index fed3a4f2adbc..000000000000
--- a/pkgs/build-support/trivial-builders/test/writeReferenceClosureToFile-mixed.nix
+++ /dev/null
@@ -1,23 +0,0 @@
-{ lib
-, runCommandLocal
-  # Test targets
-, writeClosure
-, samples
-}:
-runCommandLocal "test-trivial-builders-writeClosure-mixed" {
-  __structuredAttrs = true;
-  references = lib.mapAttrs (n: v: writeClosure [ v ]) samples;
-  allRefs = writeClosure (lib.attrValues samples);
-  inherit samples;
-  meta.maintainers = with lib.maintainers; [
-    ShamrockLee
-  ];
-} ''
-  set -eu -o pipefail
-  echo >&2 Testing mixed closures...
-  echo >&2 Checking all samples "(''${samples[*]})" "$allRefs"
-  diff -U3 \
-    <(sort <"$allRefs") \
-    <(cat "''${references[@]}" | sort | uniq)
-  touch "$out"
-''