diff --git a/sandbox/container_test.go b/sandbox/container_test.go
index 1306360..ddacbcb 100644
--- a/sandbox/container_test.go
+++ b/sandbox/container_test.go
@@ -117,11 +117,14 @@ func TestContainer(t *testing.T) {
 				mnt = append(mnt, &check.Mntent{FSName: "\x00", Dir: name, Type: "\x00", Opts: "\x00", Freq: -1, Passno: -1})
 			}
 			mnt = append(mnt, &check.Mntent{FSName: "proc", Dir: "/proc", Type: "proc", Opts: "rw,nosuid,nodev,noexec,relatime"})
-			mntentWant := new(bytes.Buffer)
-			if err := json.NewEncoder(mntentWant).Encode(mnt); err != nil {
-				t.Fatalf("cannot serialise mntent: %v", err)
+			want := new(bytes.Buffer)
+			if err := json.NewEncoder(want).Encode(&check.TestCase{
+				Mount:   mnt,
+				Seccomp: true,
+			}); err != nil {
+				t.Fatalf("cannot serialise want: %v", err)
 			}
-			container.Stdin = mntentWant
+			container.Stdin = want
 
 			// needs /proc to check mntent
 			container.Proc("/proc")
@@ -185,8 +188,7 @@ func TestHelperCheckContainer(t *testing.T) {
 			t.Errorf("/etc/hostname: %q, want %q", string(p), os.Args[5])
 		}
 	})
-	t.Run("seccomp", func(t *testing.T) { check.MustAssertSeccomp() })
-	t.Run("mntent", func(t *testing.T) { check.MustAssertMounts("", "/proc/mounts", "/proc/self/fd/0") })
+	t.Run("sandbox", func(t *testing.T) { (&check.T{PMountsPath: "/proc/mounts"}).MustCheckFile("/proc/self/fd/0") })
 }
 
 func commandContext(ctx context.Context) *exec.Cmd {
diff --git a/test/configuration.nix b/test/configuration.nix
index f6c3d14..6bdc13e 100644
--- a/test/configuration.nix
+++ b/test/configuration.nix
@@ -4,6 +4,12 @@
   config,
   ...
 }:
+let
+  testCases = import ./sandbox/case {
+    inherit (pkgs) lib callPackage foot;
+    inherit (config.environment.fortify.package) version;
+  };
+in
 {
   users.users = {
     alice = {
@@ -102,21 +108,8 @@
     home-manager = _: _: { home.stateVersion = "23.05"; };
 
     apps = [
-      {
-        name = "check-sandbox";
-        verbose = true;
-        share = pkgs.foot;
-        packages = [ ];
-        command = "${pkgs.callPackage ./sandbox {
-          inherit (config.environment.fortify.package) version;
-        }}";
-        extraPaths = [
-          {
-            src = "/proc/mounts";
-            dst = "/.fortify/mounts";
-          }
-        ];
-      }
+      testCases.moduleDefault
+
       {
         name = "ne-foot";
         verbose = true;
diff --git a/test/sandbox/assert.go b/test/sandbox/assert.go
index 3a7b31e..99ac9e8 100644
--- a/test/sandbox/assert.go
+++ b/test/sandbox/assert.go
@@ -5,6 +5,7 @@ import (
 	"io/fs"
 	"log"
 	"os"
+	"slices"
 )
 
 var (
@@ -16,76 +17,103 @@ var (
 func printf(format string, v ...any) { printfFunc(format, v...) }
 func fatalf(format string, v ...any) { fatalfFunc(format, v...) }
 
-func mustDecode(wantFile string, v any) {
-	if f, err := os.Open(wantFile); err != nil {
-		fatalf("cannot open %q: %v", wantFile, err)
-	} else if err = json.NewDecoder(f).Decode(v); err != nil {
-		fatalf("cannot decode %q: %v", wantFile, err)
-	} else if err = f.Close(); err != nil {
-		fatalf("cannot close %q: %v", wantFile, err)
-	}
+type TestCase struct {
+	FS      *FS       `json:"fs"`
+	Mount   []*Mntent `json:"mount"`
+	Seccomp bool      `json:"seccomp"`
 }
 
-func MustAssertMounts(name, hostMountsFile, wantFile string) {
-	hostMounts := make([]*Mntent, 0, 128)
-	if err := IterMounts(hostMountsFile, func(e *Mntent) {
-		hostMounts = append(hostMounts, e)
-	}); err != nil {
-		fatalf("cannot parse host mounts: %v", err)
+type T struct {
+	FS fs.FS
+
+	MountsPath, PMountsPath string
+}
+
+func (t *T) MustCheckFile(wantFilePath string) {
+	var want *TestCase
+	mustDecode(wantFilePath, &want)
+	t.MustCheck(want)
+}
+
+func (t *T) MustCheck(want *TestCase) {
+	if want.FS != nil && t.FS != nil {
+		if err := want.FS.Compare(".", t.FS); err != nil {
+			fatalf("%v", err)
+		}
+	} else {
+		printf("[SKIP] skipping fs check")
 	}
 
-	var want []Mntent
-	mustDecode(wantFile, &want)
+	if want.Mount != nil && t.PMountsPath != "" {
+		pm := mustOpenMounts(t.PMountsPath)
+		passthruMounts := slices.AppendSeq(make([]*Mntent, 0, 128), pm.Entries())
+		if err := pm.Err(); err != nil {
+			fatalf("cannot parse host mounts: %v", err)
+		}
 
-	for i := range want {
-		if want[i].Opts == "host_passthrough" {
-			for _, ent := range hostMounts {
-				if want[i].FSName == ent.FSName && want[i].Type == ent.Type {
-					// special case for tmpfs bind mounts
-					if want[i].FSName == "tmpfs" && want[i].Dir != ent.Dir {
-						continue
+		for _, e := range want.Mount {
+			if e.Opts == "host_passthrough" {
+				for _, ent := range passthruMounts {
+					if e.FSName == ent.FSName && e.Type == ent.Type {
+						// special case for tmpfs bind mounts
+						if e.FSName == "tmpfs" && e.Dir != ent.Dir {
+							continue
+						}
+
+						e.Opts = ent.Opts
+						goto out
 					}
-
-					want[i].Opts = ent.Opts
-					goto out
 				}
+				fatalf("host passthrough missing %q", e.FSName)
+			out:
 			}
-			fatalf("host passthrough missing %q", want[i].FSName)
-		out:
 		}
+
+		f := mustOpenMounts(t.MountsPath)
+		i := 0
+		for e := range f.Entries() {
+			if i == len(want.Mount) {
+				fatalf("got more than %d entries", i)
+			}
+			if !e.Is(want.Mount[i]) {
+				fatalf("entry %d\n got: %s\nwant: %s", i,
+					e, want.Mount[i])
+			}
+			printf("[ OK ] %s", e)
+
+			i++
+		}
+		if err := f.Err(); err != nil {
+			fatalf("cannot parse mounts: %v", err)
+		}
+	} else {
+		printf("[SKIP] skipping mounts check")
 	}
 
-	i := 0
-	if err := IterMounts(name, func(e *Mntent) {
-		if i == len(want) {
-			fatalf("got more than %d entries", i)
+	if want.Seccomp {
+		if TrySyscalls() != nil {
+			os.Exit(1)
 		}
-		if !e.Is(&want[i]) {
-			fatalf("entry %d\n got: %s\nwant: %s", i,
-				e, &want[i])
-		}
-
-		printf("%s", e)
-		i++
-	}); err != nil {
-		fatalf("cannot iterate mounts: %v", err)
+	} else {
+		printf("[SKIP] skipping seccomp check")
 	}
 }
 
-func MustAssertFS(e fs.FS, wantFile string) {
-	var want *FS
-	mustDecode(wantFile, &want)
-	if want == nil {
-		fatalf("invalid payload")
-	}
-
-	if err := want.Compare(".", e); err != nil {
-		fatalf("%v", err)
+func mustDecode(wantFilePath string, v any) {
+	if f, err := os.Open(wantFilePath); err != nil {
+		fatalf("cannot open %q: %v", wantFilePath, err)
+	} else if err = json.NewDecoder(f).Decode(v); err != nil {
+		fatalf("cannot decode %q: %v", wantFilePath, err)
+	} else if err = f.Close(); err != nil {
+		fatalf("cannot close %q: %v", wantFilePath, err)
 	}
 }
 
-func MustAssertSeccomp() {
-	if TrySyscalls() != nil {
-		os.Exit(1)
+func mustOpenMounts(name string) *MountsFile {
+	if f, err := OpenMounts(name); err != nil {
+		fatalf("cannot open mounts %q: %v", name, err)
+		panic("unreachable")
+	} else {
+		return f
 	}
 }
diff --git a/test/sandbox/seccomp.nix b/test/sandbox/assert.nix
similarity index 57%
rename from test/sandbox/seccomp.nix
rename to test/sandbox/assert.nix
index 3cf9b58..d45e4cb 100644
--- a/test/sandbox/seccomp.nix
+++ b/test/sandbox/assert.nix
@@ -3,18 +3,22 @@
   buildGoModule,
 
   version,
+  name,
+  want,
 }:
 let
+  wantFile = writeText "fortify-${name}-want.json" (builtins.toJSON want);
   mainFile = writeText "main.go" ''
     package main
 
+    import "os"
     import "git.gensokyo.uk/security/fortify/test/sandbox"
 
-    func main() { sandbox.MustAssertSeccomp() }
+    func main() { (&sandbox.T{FS: os.DirFS("/"), PMountsPath: "/.fortify/mounts"}).MustCheckFile("${wantFile}") }
   '';
 in
 buildGoModule {
-  pname = "check-seccomp";
+  pname = "fortify-${name}-check-sandbox";
   inherit version;
 
   src = ../.;
diff --git a/test/sandbox/case/default.nix b/test/sandbox/case/default.nix
new file mode 100644
index 0000000..b65b6ed
--- /dev/null
+++ b/test/sandbox/case/default.nix
@@ -0,0 +1,57 @@
+{
+  lib,
+  callPackage,
+  foot,
+
+  version,
+}:
+let
+  fs = mode: dir: data: {
+    mode = lib.fromHexString mode;
+    inherit
+      dir
+      data
+      ;
+  };
+
+  ent = fsname: dir: type: opts: freq: passno: {
+    inherit
+      fsname
+      dir
+      type
+      opts
+      freq
+      passno
+      ;
+  };
+
+  callTestCase =
+    path:
+    let
+      tc = import path {
+        inherit
+          fs
+          ent
+          ;
+      };
+    in
+    {
+      name = "check-sandbox-${tc.name}";
+      verbose = true;
+      share = foot;
+      packages = [ ];
+      command = "${callPackage ../. {
+        inherit (tc) name want;
+        inherit version;
+      }}";
+      extraPaths = [
+        {
+          src = "/proc/mounts";
+          dst = "/.fortify/mounts";
+        }
+      ];
+    };
+in
+{
+  moduleDefault = callTestCase ./module-default.nix;
+}
diff --git a/test/sandbox/fs.nix b/test/sandbox/case/module-default.nix
similarity index 66%
rename from test/sandbox/fs.nix
rename to test/sandbox/case/module-default.nix
index 9714a82..caca674 100644
--- a/test/sandbox/fs.nix
+++ b/test/sandbox/case/module-default.nix
@@ -1,22 +1,9 @@
+{ fs, ent }:
 {
-  lib,
-  writeText,
-  buildGoModule,
+  name = "module-default";
 
-  version,
-}:
-let
-  wantFS =
-    let
-      fs = mode: dir: data: {
-        mode = lib.fromHexString mode;
-        inherit
-          dir
-          data
-          ;
-      };
-    in
-    fs "dead" {
+  want = {
+    fs = fs "dead" {
       ".fortify" = fs "800001ed" {
         etc = fs "800001ed" null null;
         sbin = fs "800001c0" {
@@ -191,24 +178,45 @@ let
       } null;
     } null;
 
-  mainFile = writeText "main.go" ''
-    package main
+    mount = [
+      (ent "tmpfs" "/" "tmpfs" "rw,nosuid,nodev,relatime,uid=1000001,gid=1000001" 0 0)
+      (ent "proc" "/proc" "proc" "rw,nosuid,nodev,noexec,relatime" 0 0)
+      (ent "tmpfs" "/.fortify" "tmpfs" "rw,nosuid,nodev,relatime,size=4k,mode=755,uid=1000001,gid=1000001" 0 0)
+      (ent "tmpfs" "/dev" "tmpfs" "rw,nosuid,nodev,relatime,mode=755,uid=1000001,gid=1000001" 0 0)
+      (ent "devtmpfs" "/dev/null" "devtmpfs" "host_passthrough" 0 0)
+      (ent "devtmpfs" "/dev/zero" "devtmpfs" "host_passthrough" 0 0)
+      (ent "devtmpfs" "/dev/full" "devtmpfs" "host_passthrough" 0 0)
+      (ent "devtmpfs" "/dev/random" "devtmpfs" "host_passthrough" 0 0)
+      (ent "devtmpfs" "/dev/urandom" "devtmpfs" "host_passthrough" 0 0)
+      (ent "devtmpfs" "/dev/tty" "devtmpfs" "host_passthrough" 0 0)
+      (ent "devpts" "/dev/pts" "devpts" "rw,nosuid,noexec,relatime,mode=620,ptmxmode=666" 0 0)
+      (ent "mqueue" "/dev/mqueue" "mqueue" "rw,relatime" 0 0)
+      (ent "/dev/disk/by-label/nixos" "/bin" "ext4" "ro,nosuid,nodev,relatime" 0 0)
+      (ent "/dev/disk/by-label/nixos" "/usr/bin" "ext4" "ro,nosuid,nodev,relatime" 0 0)
+      (ent "overlay" "/nix/store" "overlay" "ro,nosuid,nodev,relatime,lowerdir=/mnt-root/nix/.ro-store,upperdir=/mnt-root/nix/.rw-store/upper,workdir=/mnt-root/nix/.rw-store/work,uuid=on" 0 0)
+      (ent "overlay" "/run/current-system" "overlay" "ro,nosuid,nodev,relatime,lowerdir=/mnt-root/nix/.ro-store,upperdir=/mnt-root/nix/.rw-store/upper,workdir=/mnt-root/nix/.rw-store/work,uuid=on" 0 0)
+      (ent "sysfs" "/sys/block" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
+      (ent "sysfs" "/sys/bus" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
+      (ent "sysfs" "/sys/class" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
+      (ent "sysfs" "/sys/dev" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
+      (ent "sysfs" "/sys/devices" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
+      (ent "overlay" "/run/opengl-driver" "overlay" "ro,nosuid,nodev,relatime,lowerdir=/mnt-root/nix/.ro-store,upperdir=/mnt-root/nix/.rw-store/upper,workdir=/mnt-root/nix/.rw-store/work,uuid=on" 0 0)
+      (ent "devtmpfs" "/dev/dri" "devtmpfs" "host_passthrough" 0 0)
+      (ent "proc" "/.fortify/mounts" "proc" "ro,nosuid,nodev,noexec,relatime" 0 0)
+      (ent "/dev/disk/by-label/nixos" "/.fortify/etc" "ext4" "ro,nosuid,nodev,relatime" 0 0)
+      (ent "tmpfs" "/run/user" "tmpfs" "rw,nosuid,nodev,relatime,size=1024k,mode=755,uid=1000001,gid=1000001" 0 0)
+      (ent "tmpfs" "/run/user/65534" "tmpfs" "rw,nosuid,nodev,relatime,size=8192k,mode=755,uid=1000001,gid=1000001" 0 0)
+      (ent "/dev/disk/by-label/nixos" "/tmp" "ext4" "rw,nosuid,nodev,relatime" 0 0)
+      (ent "/dev/disk/by-label/nixos" "/var/lib/fortify/u0/a1" "ext4" "rw,nosuid,nodev,relatime" 0 0)
+      (ent "tmpfs" "/etc/passwd" "tmpfs" "ro,nosuid,nodev,relatime,uid=1000001,gid=1000001" 0 0)
+      (ent "tmpfs" "/etc/group" "tmpfs" "ro,nosuid,nodev,relatime,uid=1000001,gid=1000001" 0 0)
+      (ent "/dev/disk/by-label/nixos" "/run/user/65534/wayland-0" "ext4" "ro,nosuid,nodev,relatime" 0 0)
+      (ent "tmpfs" "/run/user/65534/pulse/native" "tmpfs" "host_passthrough" 0 0)
+      (ent "/dev/disk/by-label/nixos" "/run/user/65534/bus" "ext4" "ro,nosuid,nodev,relatime" 0 0)
+      (ent "tmpfs" "/var/run/nscd" "tmpfs" "rw,nosuid,nodev,relatime,size=8k,mode=755,uid=1000001,gid=1000001" 0 0)
+      (ent "overlay" "/.fortify/sbin/fortify" "overlay" "ro,nosuid,nodev,relatime,lowerdir=/mnt-root/nix/.ro-store,upperdir=/mnt-root/nix/.rw-store/upper,workdir=/mnt-root/nix/.rw-store/work,uuid=on" 0 0)
+    ];
 
-    import "os"
-    import "git.gensokyo.uk/security/fortify/test/sandbox"
-
-    func main() { sandbox.MustAssertFS(os.DirFS("/"), "${writeText "want-fs.json" (builtins.toJSON wantFS)}") }
-  '';
-in
-buildGoModule {
-  pname = "check-fs";
-  inherit version;
-
-  src = ../.;
-  vendorHash = null;
-
-  preBuild = ''
-    go mod init git.gensokyo.uk/security/fortify/test >& /dev/null
-    cp ${mainFile} main.go
-  '';
+    seccomp = true;
+  };
 }
diff --git a/test/sandbox/default.nix b/test/sandbox/default.nix
index 8543493..9e7f12b 100644
--- a/test/sandbox/default.nix
+++ b/test/sandbox/default.nix
@@ -2,13 +2,12 @@
   writeShellScript,
   callPackage,
 
+  name,
   version,
+  want,
 }:
-writeShellScript "check-sandbox" ''
+writeShellScript "fortify-${name}-check-sandbox-script" ''
   set -e
-  ${callPackage ./mount.nix { inherit version; }}/bin/test
-  ${callPackage ./fs.nix { inherit version; }}/bin/test
-  ${callPackage ./seccomp.nix { inherit version; }}/bin/test
-
+  ${callPackage ./assert.nix { inherit name version want; }}/bin/test
   touch /tmp/sandbox-ok
 ''
diff --git a/test/sandbox/fs_test.go b/test/sandbox/fs_test.go
index 5ac31df..1262dda 100644
--- a/test/sandbox/fs_test.go
+++ b/test/sandbox/fs_test.go
@@ -75,10 +75,4 @@ func TestCompare(t *testing.T) {
 			}
 		})
 	}
-
-	t.Run("assert", func(t *testing.T) {
-		oldFatal := sandbox.SwapFatal(t.Fatalf)
-		t.Cleanup(func() { sandbox.SwapFatal(oldFatal) })
-		sandbox.MustAssertFS(make(fstest.MapFS), sandbox.MustWantFile(t, &sandbox.FS{Mode: 0xDEADBEEF}))
-	})
 }
diff --git a/test/sandbox/mount.go b/test/sandbox/mount.go
index 9a3b58c..d65824f 100644
--- a/test/sandbox/mount.go
+++ b/test/sandbox/mount.go
@@ -12,6 +12,7 @@ import "C"
 
 import (
 	"fmt"
+	"iter"
 	"runtime"
 	"sync"
 	"unsafe"
@@ -49,21 +50,38 @@ func (e *Mntent) Is(want *Mntent) bool {
 		(e.Passno == want.Passno || want.Passno == -1)
 }
 
-func IterMounts(name string, f func(e *Mntent)) error {
-	m := new(mounts)
-	m.p = name
-	if err := m.open(); err != nil {
-		return err
-	}
+type MountsFile struct {
+	m    *mounts
+	mu   sync.Mutex
+	done bool
+}
 
-	for m.scan() {
-		e := new(Mntent)
-		m.copy(e)
-		f(e)
-	}
+func OpenMounts(name string) (*MountsFile, error) {
+	f := new(MountsFile)
+	f.m = new(mounts)
+	f.m.p = name
+	return f, f.m.open()
+}
 
-	m.close()
-	return m.Err()
+func (f *MountsFile) Err() error { return f.m.Err() }
+func (f *MountsFile) Entries() iter.Seq[*Mntent] {
+	return func(yield func(*Mntent) bool) {
+		f.mu.Lock()
+		defer f.mu.Unlock()
+		if f.done {
+			return
+		}
+
+		for f.m.scan() {
+			e := new(Mntent)
+			f.m.copy(e)
+			if !yield(e) {
+				return
+			}
+		}
+		f.done = true
+		f.m.close()
+	}
 }
 
 type mounts struct {
diff --git a/test/sandbox/mount.nix b/test/sandbox/mount.nix
deleted file mode 100644
index 0c1bda1..0000000
--- a/test/sandbox/mount.nix
+++ /dev/null
@@ -1,79 +0,0 @@
-{
-  writeText,
-  buildGoModule,
-
-  version,
-}:
-let
-  wantMounts =
-    let
-      ent = fsname: dir: type: opts: freq: passno: {
-        inherit
-          fsname
-          dir
-          type
-          opts
-          freq
-          passno
-          ;
-      };
-    in
-    [
-      (ent "tmpfs" "/" "tmpfs" "rw,nosuid,nodev,relatime,uid=1000001,gid=1000001" 0 0)
-      (ent "proc" "/proc" "proc" "rw,nosuid,nodev,noexec,relatime" 0 0)
-      (ent "tmpfs" "/.fortify" "tmpfs" "rw,nosuid,nodev,relatime,size=4k,mode=755,uid=1000001,gid=1000001" 0 0)
-      (ent "tmpfs" "/dev" "tmpfs" "rw,nosuid,nodev,relatime,mode=755,uid=1000001,gid=1000001" 0 0)
-      (ent "devtmpfs" "/dev/null" "devtmpfs" "host_passthrough" 0 0)
-      (ent "devtmpfs" "/dev/zero" "devtmpfs" "host_passthrough" 0 0)
-      (ent "devtmpfs" "/dev/full" "devtmpfs" "host_passthrough" 0 0)
-      (ent "devtmpfs" "/dev/random" "devtmpfs" "host_passthrough" 0 0)
-      (ent "devtmpfs" "/dev/urandom" "devtmpfs" "host_passthrough" 0 0)
-      (ent "devtmpfs" "/dev/tty" "devtmpfs" "host_passthrough" 0 0)
-      (ent "devpts" "/dev/pts" "devpts" "rw,nosuid,noexec,relatime,mode=620,ptmxmode=666" 0 0)
-      (ent "mqueue" "/dev/mqueue" "mqueue" "rw,relatime" 0 0)
-      (ent "/dev/disk/by-label/nixos" "/bin" "ext4" "ro,nosuid,nodev,relatime" 0 0)
-      (ent "/dev/disk/by-label/nixos" "/usr/bin" "ext4" "ro,nosuid,nodev,relatime" 0 0)
-      (ent "overlay" "/nix/store" "overlay" "ro,nosuid,nodev,relatime,lowerdir=/mnt-root/nix/.ro-store,upperdir=/mnt-root/nix/.rw-store/upper,workdir=/mnt-root/nix/.rw-store/work,uuid=on" 0 0)
-      (ent "overlay" "/run/current-system" "overlay" "ro,nosuid,nodev,relatime,lowerdir=/mnt-root/nix/.ro-store,upperdir=/mnt-root/nix/.rw-store/upper,workdir=/mnt-root/nix/.rw-store/work,uuid=on" 0 0)
-      (ent "sysfs" "/sys/block" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
-      (ent "sysfs" "/sys/bus" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
-      (ent "sysfs" "/sys/class" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
-      (ent "sysfs" "/sys/dev" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
-      (ent "sysfs" "/sys/devices" "sysfs" "ro,nosuid,nodev,noexec,relatime" 0 0)
-      (ent "overlay" "/run/opengl-driver" "overlay" "ro,nosuid,nodev,relatime,lowerdir=/mnt-root/nix/.ro-store,upperdir=/mnt-root/nix/.rw-store/upper,workdir=/mnt-root/nix/.rw-store/work,uuid=on" 0 0)
-      (ent "devtmpfs" "/dev/dri" "devtmpfs" "host_passthrough" 0 0)
-      (ent "proc" "/.fortify/mounts" "proc" "ro,nosuid,nodev,noexec,relatime" 0 0)
-      (ent "/dev/disk/by-label/nixos" "/.fortify/etc" "ext4" "ro,nosuid,nodev,relatime" 0 0)
-      (ent "tmpfs" "/run/user" "tmpfs" "rw,nosuid,nodev,relatime,size=1024k,mode=755,uid=1000001,gid=1000001" 0 0)
-      (ent "tmpfs" "/run/user/65534" "tmpfs" "rw,nosuid,nodev,relatime,size=8192k,mode=755,uid=1000001,gid=1000001" 0 0)
-      (ent "/dev/disk/by-label/nixos" "/tmp" "ext4" "rw,nosuid,nodev,relatime" 0 0)
-      (ent "/dev/disk/by-label/nixos" "/var/lib/fortify/u0/a1" "ext4" "rw,nosuid,nodev,relatime" 0 0)
-      (ent "tmpfs" "/etc/passwd" "tmpfs" "ro,nosuid,nodev,relatime,uid=1000001,gid=1000001" 0 0)
-      (ent "tmpfs" "/etc/group" "tmpfs" "ro,nosuid,nodev,relatime,uid=1000001,gid=1000001" 0 0)
-      (ent "/dev/disk/by-label/nixos" "/run/user/65534/wayland-0" "ext4" "ro,nosuid,nodev,relatime" 0 0)
-      (ent "tmpfs" "/run/user/65534/pulse/native" "tmpfs" "host_passthrough" 0 0)
-      (ent "/dev/disk/by-label/nixos" "/run/user/65534/bus" "ext4" "ro,nosuid,nodev,relatime" 0 0)
-      (ent "tmpfs" "/var/run/nscd" "tmpfs" "rw,nosuid,nodev,relatime,size=8k,mode=755,uid=1000001,gid=1000001" 0 0)
-      (ent "overlay" "/.fortify/sbin/fortify" "overlay" "ro,nosuid,nodev,relatime,lowerdir=/mnt-root/nix/.ro-store,upperdir=/mnt-root/nix/.rw-store/upper,workdir=/mnt-root/nix/.rw-store/work,uuid=on" 0 0)
-    ];
-
-  mainFile = writeText "main.go" ''
-    package main
-
-    import "git.gensokyo.uk/security/fortify/test/sandbox"
-
-    func main() { sandbox.MustAssertMounts("", "/.fortify/mounts", "${writeText "want-mounts.json" (builtins.toJSON wantMounts)}") }
-  '';
-in
-buildGoModule {
-  pname = "check-mounts";
-  inherit version;
-
-  src = ../.;
-  vendorHash = null;
-
-  preBuild = ''
-    go mod init git.gensokyo.uk/security/fortify/test >& /dev/null
-    cp ${mainFile} main.go
-  '';
-}
diff --git a/test/sandbox/mount_test.go b/test/sandbox/mount_test.go
index 47df210..23a58fb 100644
--- a/test/sandbox/mount_test.go
+++ b/test/sandbox/mount_test.go
@@ -92,27 +92,29 @@ overlay /.fortify/sbin/fortify overlay ro,nosuid,nodev,relatime,lowerdir=/mnt-ro
 		}
 
 		t.Run(tc.name, func(t *testing.T) {
+			f, err := sandbox.OpenMounts(name)
+			if err != nil {
+				t.Fatalf("OpenMounts: error = %v", err)
+			}
+
 			i := 0
-			if err := sandbox.IterMounts(name, func(e *sandbox.Mntent) {
+			for e := range f.Entries() {
 				if i == len(tc.want) {
-					t.Errorf("IterMounts: got more than %d entries", i)
+					t.Errorf("Entries: got more than %d entries", i)
 					t.FailNow()
 				}
 				if *e != tc.want[i] {
-					t.Errorf("IterMounts: entry %d\n got: %s\nwant: %s", i,
+					t.Errorf("Entries: entry %d\n got: %s\nwant: %s", i,
 						e, &tc.want[i])
 					t.FailNow()
 				}
-				i++
-			}); err != nil {
-				t.Fatalf("IterMounts: error = %v", err)
-			}
-		})
 
-		t.Run(tc.name+" assert", func(t *testing.T) {
-			oldFatal := sandbox.SwapFatal(t.Fatalf)
-			t.Cleanup(func() { sandbox.SwapFatal(oldFatal) })
-			sandbox.MustAssertMounts(name, name, sandbox.MustWantFile(t, tc.want))
+				i++
+			}
+
+			if err = f.Err(); err != nil {
+				t.Fatalf("MountsFile: error = %v", err)
+			}
 		})
 
 		if err := os.Remove(name); err != nil {
diff --git a/test/test.py b/test/test.py
index 99b2f16..7f106a9 100644
--- a/test/test.py
+++ b/test/test.py
@@ -102,8 +102,8 @@ if denyOutput != "fsu: uid 1001 is not in the fsurc file\n":
 if denyOutputVerbose != "fsu: uid 1001 is not in the fsurc file\nfortify: *cannot obtain uid from fsu: permission denied\n":
     raise Exception(f"unexpected deny verbose output:\n{denyOutputVerbose}")
 
-# Check sandbox state:
-swaymsg("exec check-sandbox")
+# Check sandbox outcome:
+swaymsg("exec check-sandbox-module-default")
 machine.wait_for_file("/tmp/fortify.1000/tmpdir/1/sandbox-ok", timeout=15)
 
 # Start fortify permissive defaults outside Wayland session: