Tests:

- Add failure test (to test on nixos, we ensure that it fails with
another libc implementation).

Test.hs

@@ -8,36 +8,48 @@ import Data.Text (Text)
 import Control.Monad.IO.Class (liftIO)
 import Data.List (find)
 
+currentChannel = "channel:nixos-19.03-small"
+
 -- | Utils function: run a command and returns its output.
 processOutput p args = Text.strip . Text.pack <$> readProcess (Text.unpack p) (Text.unpack <$> args) ""
 
 -- | Returns the path to the nixGLXXX binary.
-nixGLBin version = (<>("/bin/"<>version)) <$> processOutput "nix-build" ["./", "-A", version]
+getNixGLBin version = (<>("/bin/"<>version)) <$> processOutput "nix-build" ["./", "-A", version, "--arg", "pkgs", "import (fetchTarball " <> currentChannel <> ")"]
 
 -- | Returns the vendor string associated with a glxinfo wrapped by a nixGL.
-getVendorString nixGL glxinfo = do
-  output <- Text.lines <$> processOutput nixGL [glxinfo]
+getVendorString io = do
+  output <- Text.lines <$> io
   pure $ Text.unpack <$> find ("OpenGL version string"`Text.isPrefixOf`) output
 
 -- | Checks that a nixGL wrapper works with glxinfo 32 & 64 bits.
 checkOpenGL_32_64 glxinfo32 glxinfo64 vendorName nixGLName = do
-  nixGLBin <- runIO $ (<>("/bin/"<>nixGLName)) <$> processOutput "nix-build" ["./", "-A", nixGLName]
+  beforeAll (getNixGLBin nixGLName) $ do
+    it "32 bits" $ \nixGLBin -> do
+      Just vendorString <- getVendorString (processOutput nixGLBin [glxinfo32, "-B"])
+      vendorString `shouldContain` vendorName
 
-  it "32 bits" $ do
-    Just vendorString <- getVendorString nixGLBin glxinfo32
-    vendorString `shouldContain` vendorName
-
-  it "64 bits" $ do
-    Just vendorString <- getVendorString nixGLBin glxinfo64
-    vendorString `shouldContain` vendorName
+    it "64 bits" $ \nixGLBin -> do
+      Just vendorString <- getVendorString (processOutput nixGLBin [glxinfo64, "-B"])
+      vendorString `shouldContain` vendorName
 
 main = do
-  glxinfo64 <- (<>"/bin/glxinfo") <$> processOutput "nix-build" ["<nixpkgs>", "-A", "glxinfo"]
-  glxinfo32 <- (<>"/bin/glxinfo") <$> processOutput "nix-build" ["<nixpkgs>", "-A", "pkgsi686Linux.glxinfo"]
+  -- nixos-18-03 is used so hopefully it will have a different libc
+  -- than the one used in current nixOS system, so it will trigger the
+  -- driver failure.
+  glxinfo64 <- (<>"/bin/glxinfo") <$> processOutput "nix-build" [currentChannel, "-A", "glxinfo"]
+  glxinfo32 <- (<>"/bin/glxinfo") <$> processOutput "nix-build" [currentChannel, "-A", "pkgsi686Linux.glxinfo"]
 
   let checkOpenGL = checkOpenGL_32_64 glxinfo32 glxinfo64
 
   hspec $ do
+    describe "Must fail" $ do
+      it "fails with unwrapped glxinfo64" $ do
+        vendorString <- getVendorString (processOutput glxinfo64 [])
+        vendorString `shouldBe` Nothing
+
+      it "fails with unwrapped glxinfo32" $ do
+        vendorString <- getVendorString (processOutput glxinfo32 [])
+        vendorString `shouldBe` Nothing
     describe "Mesa" $ do
       checkOpenGL "Mesa" "nixGLIntel"
     describe "Nvidia - Bumblebee" $ do