tests: extract fn instantiateTestsFromStr

Fn `instantiateTests` now takes an array of strings.
It is used in the following commit.

test/run-tests.sh

@@ -193,7 +193,7 @@ buildTests() {
     # TODO-EXTERNAL:
     # Simplify and switch to pure build when `nix build` can instantiate flake function outputs
     # shellcheck disable=SC2207
-    drvs=($(nixInstantiate "pkgs.instantiateTests \"${tests[*]}\""))
+    drvs=($(nixInstantiate "pkgs.instantiateTestsFromStr \"${tests[*]}\""))
     for i in "${!tests[@]}"; do
         testName=${tests[$i]}
         drv=${drvs[$i]}

test/tests.nix

@@ -459,16 +459,15 @@ in {
           };
         });
 
+    instantiateTestsFromStr = testNamesStr: instantiateTests (lib.splitString " " testNamesStr);
+
     instantiateTests = testNames:
-      let
+      map (name:
-        testNames' = lib.splitString " " testNames;
+        let
-      in
+          test = tests.${name};
-        map (name:
+        in
-          let
+          builtins.seq (builtins.trace "Evaluating test '${name}'" test.outPath)
-            test = tests.${name};
+            test
-          in
+      ) testNames;
-            builtins.seq (builtins.trace "Evaluating test '${name}'" test.outPath)
-              test
-        ) testNames';
   };
 }