testers.testEqualArrayOrMap: move argument check from bash to Nix

pkgs/build-support/testers/testEqualArrayOrMap/build-command.sh

@@ -2,13 +2,10 @@
 
 set -eu
 
-preScript() {
-  # If neither expectedArray nor expectedMap are declared, the test is meaningless.
-  if ! isDeclaredArray expectedArray && ! isDeclaredMap expectedMap; then
-    nixErrorLog "neither expectedArray nor expectedMap were set, so test is meaningless!"
-    exit 1
-  fi
+# NOTE: If neither expectedArray nor expectedMap are declared, the test is meaningless.
+# This precondition is checked in the Nix expression through an assert.
 
+preScript() {
   if isDeclaredArray valuesArray; then
     # shellcheck disable=SC2154
     nixLog "using valuesArray: $(declare -p valuesArray)"

pkgs/build-support/testers/testEqualArrayOrMap/tester.nix

@@ -4,6 +4,7 @@
   stdenvNoCC,
 }:
 let
+  inherit (lib.asserts) assertMsg;
   inherit (lib.customisation) makeOverridable;
 
   testEqualArrayOrMap =
@@ -15,6 +16,9 @@ let
       expectedMap ? null,
       script,
     }:
+    assert assertMsg (
+      expectedArray != null || expectedMap != null
+    ) "testEqualArrayOrMap: at least one of 'expectedArray' or 'expectedMap' must be provided";
     stdenvNoCC.mkDerivation {
       __structuredAttrs = true;
       strictDeps = true;