tests.nixpkgs-check-by-name: Use real lib for tests

This way we can also detect regressions caused by lib

pkgs/test/nixpkgs-check-by-name/src/main.rs

@@ -226,7 +226,9 @@ mod tests {
     }
 
     fn test_nixpkgs(name: &str, path: &Path, expected_errors: &str) -> anyhow::Result<()> {
-        let extra_nix_path = Path::new("tests/mock-nixpkgs.nix");
+        let mock_nixpkgs_path = Path::new("tests/mock-nixpkgs.nix");
+        let real_lib_path = Path::new("../../../lib");
+        let extra_nix_path = [mock_nixpkgs_path, real_lib_path];
 
         let base_path = path.join("base");
         let base_nixpkgs = if base_path.exists() {
@@ -238,7 +240,7 @@ mod tests {
         // We don't want coloring to mess up the tests
         let writer = temp_env::with_var("NO_COLOR", Some("1"), || -> anyhow::Result<_> {
             let mut writer = vec![];
-            process(base_nixpkgs, &path, &[&extra_nix_path], &mut writer)
+            process(base_nixpkgs, &path, &extra_nix_path, &mut writer)
                 .with_context(|| format!("Failed test case {name}"))?;
             Ok(writer)
         })?;

pkgs/test/nixpkgs-check-by-name/tests/mock-nixpkgs.nix

@@ -25,25 +25,7 @@ It returns a Nixpkgs-like function that can be auto-called and evaluates to an a
 let
 
   # Simplified versions of lib functions
-  lib = {
-    fix = f: let x = f x; in x;
-
-    extends = overlay: f: final:
-      let
-        prev = f final;
-      in
-      prev // overlay final prev;
-
-    callPackageWith = autoArgs: fn: args:
-      let
-        f = if builtins.isFunction fn then fn else import fn;
-        fargs = builtins.functionArgs f;
-        allArgs = builtins.intersectAttrs fargs autoArgs // args;
-      in
-      f allArgs;
-
-    isDerivation = value: value.type or null == "derivation";
-  };
+  lib = import ../../../../lib;
 
   # The base fixed-point function to populate the resulting attribute set
   pkgsFun = self: {