Restore now-working build-remote-content-addressed-fixed test

This was

 - Added in dbf96e10ec.

 - Commented out in 07975979aa, which I
   believe only reached master by mistake.

 - Deleted in c32168c9bc, when
   `tests/build-hook-ca.nix` was reused for a new test.

But the test works, and we ought to have it.

tests/build-hook-ca-fixed.nix

@@ -0,0 +1,56 @@
+{ busybox }:
+
+with import ./config.nix;
+
+let
+
+  mkDerivation = args:
+    derivation ({
+      inherit system;
+      builder = busybox;
+      args = ["sh" "-e" args.builder or (builtins.toFile "builder-${args.name}.sh" "if [ -e .attrs.sh ]; then source .attrs.sh; fi; eval \"$buildCommand\"")];
+      outputHashMode = "recursive";
+      outputHashAlgo = "sha256";
+    } // removeAttrs args ["builder" "meta"])
+    // { meta = args.meta or {}; };
+
+  input1 = mkDerivation {
+    shell = busybox;
+    name = "build-remote-input-1";
+    buildCommand = "echo FOO > $out";
+    requiredSystemFeatures = ["foo"];
+    outputHash = "sha256-FePFYIlMuycIXPZbWi7LGEiMmZSX9FMbaQenWBzm1Sc=";
+  };
+
+  input2 = mkDerivation {
+    shell = busybox;
+    name = "build-remote-input-2";
+    buildCommand = "echo BAR > $out";
+    requiredSystemFeatures = ["bar"];
+    outputHash = "sha256-XArauVH91AVwP9hBBQNlkX9ccuPpSYx9o0zeIHb6e+Q=";
+  };
+
+  input3 = mkDerivation {
+    shell = busybox;
+    name = "build-remote-input-3";
+    buildCommand = ''
+      read x < ${input2}
+      echo $x BAZ > $out
+    '';
+    requiredSystemFeatures = ["baz"];
+    outputHash = "sha256-daKAcPp/+BYMQsVi/YYMlCKoNAxCNDsaivwSHgQqD2s=";
+  };
+
+in
+
+  mkDerivation {
+    shell = busybox;
+    name = "build-remote";
+    buildCommand =
+      ''
+        read x < ${input1}
+        read y < ${input3}
+        echo "$x $y" > $out
+      '';
+    outputHash = "sha256-5SxbkUw6xe2l9TE1uwCvTtTDysD1vhRor38OtDF0LqQ=";
+  }

tests/build-remote-content-addressed-fixed.sh

@@ -0,0 +1,5 @@
+source common.sh
+
+file=build-hook-ca-fixed.nix
+
+source build-remote.sh

tests/build-remote-content-addressed-floating.sh

@@ -1,6 +1,6 @@
 source common.sh
 
-file=build-hook-ca.nix
+file=build-hook-ca-floating.nix
 
 sed -i 's/experimental-features .*/& ca-derivations/' "$NIX_CONF_DIR"/nix.conf
 

tests/local.mk

@@ -17,6 +17,7 @@ nix_tests = \
   linux-sandbox.sh \
   build-dry.sh \
   build-remote-input-addressed.sh \
+  build-remote-content-addressed-fixed.sh \
   build-remote-content-addressed-floating.sh \
   ssh-relay.sh \
   nar-access.sh \