tests: Add pam_malcontent.so tests

These tests check that the built `pam_malcontent.so` module can be
loaded using `dlopen()` and that it exports the right symbol. This
should mean that PAM can load it and use it.

Unfortunately, we can’t actually run the module, since PAM hard-codes
its configuration path as being in `/etc`, and there seems to be no way
to override that to load a dummy configuration from a test directory. So
the only way to test the PAM module is to use a file system bind mount
to fake `/etc` (which requires privileges); or to actually install it on
your system and integrate it into your real PAM configuration. Neither
of those are acceptable for a unit test.

It might be possible to re-execute a test under `bwrap` (if installed)
to achieve this, bind mounting a dummy `/etc/pam.d/dummy` service file
into the subprocess’ mount namespace, and otherwise bind mounting `/` to
`/`. It would need a mock malcontent D-Bus API to talk to. Something to
experiment with another time.

(See `_pam_init_handlers()` in
https://github.com/linux-pam/linux-pam/blob/master/libpam/pam_handlers.c
for details of how PAM modules are loaded.)

Signed-off-by: Philip Withnall <withnall@endlessm.com>

pam/meson.build

@@ -20,3 +20,5 @@ pam_malcontent = shared_library('pam_malcontent',
   include_directories: root_inc,
   install: true,
   install_dir: pamlibdir)
+
+subdir('tests')

pam/tests/meson.build

@@ -0,0 +1,48 @@
+deps = [
+  dependency('glib-2.0', version: '>= 2.60.0'),
+  cc.find_library('dl'),
+]
+
+envs = test_env + [
+  'G_TEST_SRCDIR=' + meson.current_source_dir(),
+  'G_TEST_BUILDDIR=' + meson.current_build_dir(),
+]
+
+test_programs = [
+  ['pam_malcontent', [], deps],
+]
+
+installed_tests_metadir = join_paths(datadir, 'installed-tests',
+                                     'libmalcontent-' + libmalcontent_api_version)
+installed_tests_execdir = join_paths(libexecdir, 'installed-tests',
+                                     'libmalcontent-' + libmalcontent_api_version)
+
+foreach program: test_programs
+  test_conf = configuration_data()
+  test_conf.set('installed_tests_dir', installed_tests_execdir)
+  test_conf.set('program', program[0])
+
+  configure_file(
+    input: test_template,
+    output: program[0] + '.test',
+    install: enable_installed_tests,
+    install_dir: installed_tests_metadir,
+    configuration: test_conf,
+  )
+
+  exe = executable(
+    program[0],
+    [program[0] + '.c'] + program[1],
+    dependencies: program[2],
+    include_directories: root_inc,
+    install: enable_installed_tests,
+    install_dir: installed_tests_execdir,
+  )
+
+  test(
+    program[0],
+    exe,
+    env: envs,
+    args: ['--tap'],
+  )
+endforeach

pam/tests/pam_malcontent.c

@@ -0,0 +1,62 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright © 2019 Endless Mobile, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Authors:
+ *  - Philip Withnall <withnall@endlessm.com>
+ */
+
+#include <dlfcn.h>
+#include <glib.h>
+#include <locale.h>
+#include <stdlib.h>
+
+/* Test that the `pam_malcontent.so` module can be loaded using dlopen() and
+ * that it exports the appropriate symbols for PAM to be able to use it. */
+static void
+test_pam_malcontent_dlopen (void)
+{
+  g_autofree gchar *module_path = NULL;
+  void *handle;
+  int retval;
+  void *fn;
+
+  module_path = g_test_build_filename (G_TEST_BUILT, "..", "pam_malcontent.so", NULL);
+
+  /* Check the module can be loaded. */
+  handle = dlopen (module_path, RTLD_NOW);
+  g_assert_nonnull (handle);
+
+  /* Check the appropriate symbols exist. */
+  fn = dlsym (handle, "pam_sm_acct_mgmt");
+  g_assert_nonnull (fn);
+
+  retval = dlclose (handle);
+  g_assert_cmpint (retval, ==, 0);
+}
+
+int
+main (int    argc,
+      char **argv)
+{
+  setlocale (LC_ALL, "");
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/pam_malcontent/dlopen", test_pam_malcontent_dlopen);
+
+  return g_test_run ();
+}