diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/package.nix b/pkgs/by-name/ni/nixos-rebuild-ng/package.nix
index 2c630f60a843..5090b94b7157 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/package.nix
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/package.nix
@@ -1,5 +1,6 @@
 {
   lib,
+  callPackage,
   installShellFiles,
   mkShell,
   nix,
@@ -92,20 +93,23 @@ python3Packages.buildPythonApplication rec {
         '';
       };
 
-      # NOTE: this is a passthru test rather than a build-time test because we
-      # want to keep the build closures small
-      tests.ci = runCommand "${pname}-ci" { nativeBuildInputs = [ python-with-pkgs ]; } ''
-        export RUFF_CACHE_DIR="$(mktemp -d)"
+      tests = {
+        repl = callPackage ./tests/repl.nix { };
+        # NOTE: this is a passthru test rather than a build-time test because we
+        # want to keep the build closures small
+        linters = runCommand "${pname}-linters" { nativeBuildInputs = [ python-with-pkgs ]; } ''
+          export RUFF_CACHE_DIR="$(mktemp -d)"
 
-        echo -e "\x1b[32m## run mypy\x1b[0m"
-        mypy ${src}
-        echo -e "\x1b[32m## run ruff\x1b[0m"
-        ruff check ${src}
-        echo -e "\x1b[32m## run ruff format\x1b[0m"
-        ruff format --check ${src}
+          echo -e "\x1b[32m## run mypy\x1b[0m"
+          mypy ${src}
+          echo -e "\x1b[32m## run ruff\x1b[0m"
+          ruff check ${src}
+          echo -e "\x1b[32m## run ruff format\x1b[0m"
+          ruff format --check ${src}
 
-        touch $out
-      '';
+          touch $out
+        '';
+      };
     };
 
   meta = {
diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py b/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py
index e2e1cea2327d..3100496e2eee 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py
@@ -366,7 +366,8 @@ def repl_flake(attr: str, flake: Flake, **flake_flags: Args) -> None:
     expr = Template(
         files(__package__).joinpath(FLAKE_REPL_TEMPLATE).read_text()
     ).substitute(
-        flake_path=flake.path,
+        flake=flake,
+        flake_path=flake.path.resolve() if isinstance(flake.path, Path) else flake.path,
         flake_attr=flake.attr,
         bold="\033[1m",
         blue="\033[34;1m",
diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/repl.nix.template b/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/repl.nix.template
index 17db87423711..76c5ab2977ac 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/repl.nix.template
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/repl.nix.template
@@ -16,7 +16,7 @@ let
         - ${blue}lib${reset}      Nixpkgs library functions
         - other module arguments
 
-        - ${blue}flake${reset}    Flake outputs, inputs and source info of ${flake_path}
+        - ${blue}flake${reset}    Flake outputs, inputs and source info of ${flake}
 
     Use tab completion to browse around ${blue}config${reset}.
 
diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_nix.py b/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_nix.py
index 928c0e8616a8..a5310a1df8a8 100644
--- a/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_nix.py
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_nix.py
@@ -399,9 +399,9 @@ def test_repl(mock_run: Any) -> None:
 @patch(get_qualified_name(n.run_wrapper, n), autospec=True)
 def test_repl_flake(mock_run: Any) -> None:
     n.repl_flake("attr", m.Flake(Path("flake.nix"), "myAttr"), nix_flag=True)
-    # This method would be really annoying to test, and it is not that important
-    # So just check that we are at least calling it
-    assert mock_run.called
+    # See nixos-rebuild-ng.tests.repl for a better test,
+    # this is mostly for sanity check
+    assert mock_run.call_count == 1
 
 
 @patch(get_qualified_name(n.run_wrapper, n), autospec=True)
diff --git a/pkgs/by-name/ni/nixos-rebuild-ng/tests/repl.nix b/pkgs/by-name/ni/nixos-rebuild-ng/tests/repl.nix
new file mode 100644
index 000000000000..c92b7c6fff7f
--- /dev/null
+++ b/pkgs/by-name/ni/nixos-rebuild-ng/tests/repl.nix
@@ -0,0 +1,163 @@
+{
+  lib,
+  expect,
+  nix,
+  nixos-rebuild-ng,
+  path,
+  runCommand,
+  stdenv,
+  writeText,
+}:
+let
+  # Arguably not true, but it holds up for now.
+  escapeExpect = lib.strings.escapeNixString;
+
+  expectSetup = ''
+    set timeout 180
+    proc expect_simple { pattern } {
+      puts "Expecting: $pattern"
+      expect {
+        timeout {
+          puts "\nTimeout waiting for: $pattern\n"
+          exit 1
+        }
+        $pattern
+      }
+    }
+  '';
+
+  # In case we want/need to evaluate packages or the assertions or whatever,
+  # we want to have a linux system.
+  # TODO: make the non-flake test use thise.
+  linuxSystem = lib.replaceStrings [ "darwin" ] [ "linux" ] stdenv.hostPlatform.system;
+
+in
+runCommand "test-nixos-rebuild-repl"
+  {
+    nativeBuildInputs = [
+      expect
+      nix
+      (nixos-rebuild-ng.override { withNgSuffix = false; })
+    ];
+
+    nixpkgs = if builtins.pathExists (path + "/.git") then lib.cleanSource path else path;
+  }
+  ''
+    export HOME=$(mktemp -d)
+    export TEST_ROOT=$PWD/test-tmp
+
+    # Prepare for running Nix in sandbox
+    export NIX_BUILD_HOOK=
+    export NIX_CONF_DIR=$TEST_ROOT/etc
+    export NIX_LOCALSTATE_DIR=$TEST_ROOT/var
+    export NIX_LOG_DIR=$TEST_ROOT/var/log/nix
+    export NIX_STATE_DIR=$TEST_ROOT/var/nix
+    export NIX_STORE_DIR=$TEST_ROOT/store
+    export PAGER=cat
+    mkdir -p $TEST_ROOT $NIX_CONF_DIR
+
+    echo General setup
+    ##################
+
+    export NIX_PATH=nixpkgs=$nixpkgs:nixos-config=$HOME/configuration.nix
+    cat >> ~/configuration.nix <<EOF
+    {
+      boot.loader.grub.enable = false;
+      fileSystems."/".device = "x";
+      imports = [ ./hardware-configuration.nix ];
+    }
+    EOF
+
+    echo '{ }' > ~/hardware-configuration.nix
+
+
+    echo Test traditional NixOS configuration
+    #########################################
+
+    expect ${writeText "test-nixos-rebuild-repl-expect" ''
+      ${expectSetup}
+      spawn nixos-rebuild repl --fast
+
+      expect "nix-repl> "
+
+      send "config.networking.hostName\n"
+      expect "\"nixos\""
+    ''}
+
+
+    echo Test flake based NixOS configuration
+    #########################################
+
+    # Switch to flake flavored environment
+    unset NIX_PATH
+    cat > $NIX_CONF_DIR/nix.conf <<EOF
+    experimental-features = nix-command flakes
+    EOF
+
+    # Make the config pure
+    echo '{ nixpkgs.hostPlatform = "${linuxSystem}"; }' > ~/hardware-configuration.nix
+
+    cat >~/flake.nix <<EOF
+    {
+      inputs.nixpkgs.url = "path:$nixpkgs";
+      outputs = { nixpkgs, ... }: {
+        nixosConfigurations.testconf = nixpkgs.lib.nixosSystem {
+          modules = [
+            ./configuration.nix
+            # Let's change it up a bit
+            { networking.hostName = "itsme"; }
+          ];
+        };
+      };
+    }
+    EOF
+
+    # cat -n ~/flake.nix
+
+    expect ${writeText "test-nixos-rebuild-repl-absolute-path-expect" ''
+      ${expectSetup}
+      spawn sh -c "nixos-rebuild repl --fast --flake path:\$HOME#testconf"
+
+      expect_simple "nix-repl>"
+
+      send "config.networking.hostName\n"
+      expect_simple "itsme"
+
+      expect_simple "nix-repl>"
+      send "lib.version\n"
+      expect_simple ${
+        escapeExpect (
+          # The version string is a bit different in the flake lib, so we expect a prefix and ignore the rest
+          # Furthermore, including the revision (suffix) would cause unnecessary rebuilds.
+          # Note that a length of 4 only matches e.g. "24.
+          lib.strings.substring 0 4 (lib.strings.escapeNixString lib.version)
+        )
+      }
+
+      # Make sure it's the right lib - should be the flake lib, not Nixpkgs lib.
+      expect_simple "nix-repl>"
+      send "lib?nixosSystem\n"
+      expect_simple "true"
+      expect_simple "nix-repl>"
+      send "lib?nixos\n"
+      expect_simple "true"
+    ''}
+
+    pushd "$HOME"
+    expect ${writeText "test-nixos-rebuild-repl-relative-path-expect" ''
+      ${expectSetup}
+      spawn sh -c "nixos-rebuild repl --fast --flake .#testconf"
+
+      expect_simple "nix-repl>"
+
+      send "config.networking.hostName\n"
+      expect_simple "itsme"
+    ''}
+    popd
+
+    echo
+
+    #########
+    echo Done
+    touch $out
+  ''