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diff --git a/tests/programs.c b/tests/programs.c
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+# Copyright (C) 2015  Codethink Limited
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; version 2 of the License.
+#
+# This program 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 General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+
+'''Test programs for 'sandboxlib' functional tests.
+
+The tests need to create clean, reproducible sandboxes in order for the tests
+to behave the same on all machines. This means not depending on the host OS.
+We need some programs to actually run inside the sandbox and try to break them.
+There are two approaches: either build / download a small OS from somewhere
+that will run in a chroot and will work the same on all platforms, or build
+minimal, self-contained tester programs using tools in the host OS.
+
+I picked the second approach: to test the sandboxes using statically linked C
+programs. Each C program below should be small, self-contained and should test
+one thing.
+
+'''
+
+
+def build_c_program(source_code, output_path, compiler_args=None):
+    '''Compile a temporary C program.'''
+    compiler_args = compiler_args or []
+    with tempfile.NamedTemporaryFile(suffix='.c') as f:
+        f.write(WRITEABLE_PATHS_TEST_CODE.encode('utf-8'))
+        f.flush()
+
+        subprocess.check_call(
+            ['gcc', '-static', f.name, '-o', str(output_path)])
+
+
+# Test if a file or directory exists.
+FILE_OR_DIRECTORY_EXISTS_TEST_PROGRAM = """
+#include <stdio.h>
+#include <sys/stat.h>
+
+int main(int argc, char *argv[]) {
+    struct stat stat_data;
+
+    if (argc != 2) {
+        fprintf(stderr, "Expected 1 argument: filename to try to read from.");
+        return 1;
+    }
+
+    if (stat(argv[1], &stat_data) != 0) {
+        printf("Did not find %s.", argv[1]);
+        return 2;
+    }
+
+    printf("%s exists", argv[1]);
+    return 0;
+};
+"""
+
+@pytest.fixture(scope='module')
+def file_exists_test_program(self, tmpdir):
+    program_path = tmpdir.join('writable-paths-tester')
+    build_c_program(
+        FILE_OR_DIRECTORY_EXISTS_TEST_PROGRAM, program_path, compiler_args=['-static'])
+    return program_path
+
+# Test if a file can be written to.
+FILE_IS_WRITABLE_TEST_PROGRAM = """
+#include <stdio.h>
+
+int main(int argc, char *argv[]) {
+    FILE *file;
+
+    if (argc != 2) {
+        fprintf(stderr, "Expected 1 argument: filename to try to write to.");
+        return 1;
+    }
+
+    file = fopen(argv[0], "w");
+
+    if (file == NULL) {
+        printf("Couldn't open %s for writing.", argv[1]);
+        return 2;
+    }
+
+    if (fputc('!', file) != '!') {
+        printf("Couldn't write to %s.", argv[1]);
+        fclose(file);
+        return 3;
+    }
+
+    fclose(file);
+    printf("Wrote data to %s.", argv[1]);
+    return 0;
+};
+"""
+
+@pytest.fixture(scope='module')
+def file_is_writable_test_program(self, tmpdir):
+    program_path = tmpdir.join('writable-paths-tester')
+    build_c_program(
+        FILE_IS_WRITEABLE_TEST_PROGRAM, program_path, compiler_args=['-static'])
+    return program_path