diff --git a/flake.nix b/flake.nix
index f7d64c38..eb807273 100644
--- a/flake.nix
+++ b/flake.nix
@@ -35,6 +35,24 @@
         overrideInputs."haskell-parsers" = ./nix/haskell-parsers;
       };
 
+      test-simple = {
+        dir = "test/simple";
+        overrideInputs = {
+          "haskell-flake" = ./.;
+          "flake-parts" = "github:hercules-ci/flake-parts/7c7a8bce3dffe71203dcd4276504d1cb49dfe05f";
+          "nixpkgs" = "github:nixos/nixpkgs/bb31220cca6d044baa6dc2715b07497a2a7c4bc7";
+        };
+      };
+
+      test-project-module = {
+        dir = "test/project-module";
+        overrideInputs = {
+          "haskell-flake" = ./.;
+          "flake-parts" = "github:hercules-ci/flake-parts/7c7a8bce3dffe71203dcd4276504d1cb49dfe05f";
+          "nixpkgs" = "github:nixos/nixpkgs/bb31220cca6d044baa6dc2715b07497a2a7c4bc7";
+        };
+      };
+
       # Legacy shell script test
       test = {
         dir = "test";
diff --git a/runtest.sh b/runtest.sh
index 42680a3b..ff7352bd 100755
--- a/runtest.sh
+++ b/runtest.sh
@@ -10,9 +10,8 @@ nix --version
 # TODO: Supplant these scripts with Nix. See https://github.com/srid/haskell-flake/issues/241
 TESTS=(
   ./example
-  ./test/simple
+  # TODO: Move these to flake check, just like ./test/{simple, project-module}
   ./test/with-subdir
-  ./test/project-module
   # We run this separately, because it's a bit slow.
   # ./doc
 )
diff --git a/test/common.sh b/test/common.sh
index 0617f2fc..1f4ee732 100644
--- a/test/common.sh
+++ b/test/common.sh
@@ -7,7 +7,7 @@ function logHeader {
 
 nix --version
 
-SYSTEM=$(nix show-config | grep 'system =' | awk '{print $3}')
+SYSTEM=$(nix eval --impure --expr builtins.currentSystem)
 
 DIR_OF_COMMON_SH="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 HASKELL_FLAKE=${DIR_OF_COMMON_SH}/..
diff --git a/test/project-module/test.sh b/test/project-module/test.sh
deleted file mode 100755
index 383725fa..00000000
--- a/test/project-module/test.sh
+++ /dev/null
@@ -1,9 +0,0 @@
-source ../common.sh
-set -euxo pipefail
-
-# First, build the flake
-logHeader "Testing nix build"
-nix build ${OVERRIDE_ALL}
-
-logHeader "Testing nix devshell"
-nix develop ${OVERRIDE_ALL} -c echo
diff --git a/test/simple/flake.nix b/test/simple/flake.nix
index 5d337666..5d81e557 100644
--- a/test/simple/flake.nix
+++ b/test/simple/flake.nix
@@ -7,8 +7,6 @@
     flake-parts = { };
     haskell-flake = { };
 
-    check-flake.url = "github:srid/check-flake/48a17393ed4fcd523399d6602c283775b5127295";
-
     haskell-multi-nix.url = "github:srid/haskell-multi-nix/7aed736571714ec12105ec110358998d70d59e34";
     haskell-multi-nix.flake = false;
   };
@@ -17,7 +15,6 @@
       systems = nixpkgs.lib.systems.flakeExposed;
       imports = [
         inputs.haskell-flake.flakeModule
-        inputs.check-flake.flakeModule
       ];
       flake.haskellFlakeProjectModules.default = { pkgs, lib, ... }: {
         packages = {
@@ -38,7 +35,6 @@
             # Setting to null should remove this tool from defaults.
             ghcid = null;
           };
-          hlsCheck.enable = true;
         };
       };
       perSystem = { self', pkgs, lib, ... }: {
@@ -74,6 +70,52 @@
         # An explicit app to test `nix run .#test` (*without* falling back to
         # using self.packages.test)
         apps.app1 = self'.apps.haskell-flake-test;
+
+        # Our test
+        checks.test =
+          pkgs.runCommandNoCC "simple-test"
+            {
+              nativeBuildInputs = with pkgs; [
+                which
+              ] ++ self'.devShells.default.nativeBuildInputs;
+
+              # Test defaults.settings module behaviour, viz: haddock
+              NO_HADDOCK =
+                lib.assertMsg (!lib.hasAttr "doc" self'.packages.default)
+                  "doc output should not be present";
+            }
+            ''
+              (
+              set -x
+              echo "Testing test/simple ..."
+
+              # Run the cabal executable as flake app
+              ${self'.apps.app1.program} | grep fooFunc
+
+              # Setting buildTools.ghcid to null should disable that default
+              # buildTool (ghcid)
+              which ghcid && \
+                (echo "ghcid should not be in devshell"; exit 2)
+
+              # Adding a buildTool (fzf, here) should put it in devshell.
+              which fzf || \
+                (echo "fzf should be in devshell"; exit 2)
+
+              # mkShellArgs works
+              ${self'.devShells.default.shellHook}
+              if [[ "$FOO" == "bar" ]]; then 
+                  echo "$FOO"
+              else 
+                  echo "FOO is not bar" 
+                  exit 2
+              fi
+
+              # extraLibraries works
+              runghc ${./script} | grep -F 'TOML-flavored boolean: Bool True'
+
+              touch $out
+              )
+            '';
       };
     };
 }
diff --git a/test/simple/test-in-devshell.sh b/test/simple/test-in-devshell.sh
deleted file mode 100755
index 460add35..00000000
--- a/test/simple/test-in-devshell.sh
+++ /dev/null
@@ -1,29 +0,0 @@
-# This script is run in a `nix develop` shell by Github Actions.
-# 
-# You can also run it locally using:
-#
-#  nix develop --override-input haskell-flake ../ -c ./test-in-devshell.sh
-#
-# Or, just run `runtest.sh` from project root.
-
-set -xe
-
-# Test haskell devshell (via HLS check)
-haskell-language-server
-
-# Setting buildTools.ghcid to null should disable that default buildTool
-which ghcid && exit 2 || echo
-
-# Adding a buildTool (fzf, here) should put it in devshell.
-which fzf
-
-# mkShellArgs works
-if [[ "$FOO" == "bar" ]]; then 
-    echo "$FOO"
-else 
-    echo "FOO is not bar" 
-    exit 2
-fi
-
-# extraLibraries works
-runghc ./script | grep -F 'TOML-flavored boolean: Bool True'
diff --git a/test/simple/test.sh b/test/simple/test.sh
deleted file mode 100755
index 5ff9a596..00000000
--- a/test/simple/test.sh
+++ /dev/null
@@ -1,27 +0,0 @@
-source ../common.sh
-set -euxo pipefail
-
-rm -f result result-bin
-
-# First, build the flake
-logHeader "Testing nix build"
-nix build ${OVERRIDE_ALL}
-
-# Test defaults.settings module behaviour, viz: haddock
-nix build ${OVERRIDE_ALL} .#default^doc && {
-    echo "ERROR: dontHaddock (from defaults.settings) not in effect"
-    exit 1
-}
-
-# Run the devshell test script in a nix develop shell.
-logHeader "Testing nix devshell"
-nix develop ${OVERRIDE_ALL} -c ./test-in-devshell.sh
-# Run the cabal executable as flake app
-logHeader "Testing nix flake app (cabal exe)"
-nix run ${OVERRIDE_ALL} .#app1
-# Test non-devshell features:
-# Checks
-logHeader "Testing nix flake checks"
-nix --option sandbox false build \
-    --no-link --print-out-paths \
-    ${OVERRIDE_ALL} -L .#check