diff --git a/src/libutil-tests/file-system.cc b/src/libutil-tests/file-system.cc
new file mode 100644
index 000000000..2c10d4869
--- /dev/null
+++ b/src/libutil-tests/file-system.cc
@@ -0,0 +1,278 @@
+#include "util.hh"
+#include "types.hh"
+#include "file-system.hh"
+#include "processes.hh"
+#include "terminal.hh"
+#include "strings.hh"
+
+#include <limits.h>
+#include <gtest/gtest.h>
+#include <rapidcheck/gtest.h>
+
+#include <numeric>
+
+#ifdef _WIN32
+#  define FS_SEP L"\\"
+#  define FS_ROOT L"C:" FS_SEP // Need a mounted one, C drive is likely
+#else
+#  define FS_SEP "/"
+#  define FS_ROOT FS_SEP
+#endif
+
+#ifndef PATH_MAX
+#  define PATH_MAX 4096
+#endif
+
+#ifdef _WIN32
+#  define GET_CWD _wgetcwd
+#else
+#  define GET_CWD getcwd
+#endif
+
+namespace nix {
+
+/* ----------- tests for file-system.hh -------------------------------------*/
+
+/* ----------------------------------------------------------------------------
+ * absPath
+ * --------------------------------------------------------------------------*/
+
+TEST(absPath, doesntChangeRoot)
+{
+    auto p = absPath(std::filesystem::path{FS_ROOT});
+
+    ASSERT_EQ(p, FS_ROOT);
+}
+
+TEST(absPath, turnsEmptyPathIntoCWD)
+{
+    OsChar cwd[PATH_MAX + 1];
+    auto p = absPath(std::filesystem::path{""});
+
+    ASSERT_EQ(p, GET_CWD((OsChar *) &cwd, PATH_MAX));
+}
+
+TEST(absPath, usesOptionalBasePathWhenGiven)
+{
+    OsChar _cwd[PATH_MAX + 1];
+    OsChar * cwd = GET_CWD((OsChar *) &_cwd, PATH_MAX);
+
+    auto p = absPath(std::filesystem::path{""}.string(), std::filesystem::path{cwd}.string());
+
+    ASSERT_EQ(p, std::filesystem::path{cwd}.string());
+}
+
+TEST(absPath, isIdempotent)
+{
+    OsChar _cwd[PATH_MAX + 1];
+    OsChar * cwd = GET_CWD((OsChar *) &_cwd, PATH_MAX);
+    auto p1 = absPath(std::filesystem::path{cwd});
+    auto p2 = absPath(p1);
+
+    ASSERT_EQ(p1, p2);
+}
+
+TEST(absPath, pathIsCanonicalised)
+{
+    auto path = FS_ROOT OS_STR("some/path/with/trailing/dot/.");
+    auto p1 = absPath(std::filesystem::path{path});
+    auto p2 = absPath(p1);
+
+    ASSERT_EQ(p1, FS_ROOT "some" FS_SEP "path" FS_SEP "with" FS_SEP "trailing" FS_SEP "dot");
+    ASSERT_EQ(p1, p2);
+}
+
+/* ----------------------------------------------------------------------------
+ * canonPath
+ * --------------------------------------------------------------------------*/
+
+TEST(canonPath, removesTrailingSlashes)
+{
+    std::filesystem::path path = FS_ROOT "this/is/a/path//";
+    auto p = canonPath(path.string());
+
+    ASSERT_EQ(p, std::filesystem::path{FS_ROOT "this" FS_SEP "is" FS_SEP "a" FS_SEP "path"}.string());
+}
+
+TEST(canonPath, removesDots)
+{
+    std::filesystem::path path = FS_ROOT "this/./is/a/path/./";
+    auto p = canonPath(path.string());
+
+    ASSERT_EQ(p, std::filesystem::path{FS_ROOT "this" FS_SEP "is" FS_SEP "a" FS_SEP "path"}.string());
+}
+
+TEST(canonPath, removesDots2)
+{
+    std::filesystem::path path = FS_ROOT "this/a/../is/a////path/foo/..";
+    auto p = canonPath(path.string());
+
+    ASSERT_EQ(p, std::filesystem::path{FS_ROOT "this" FS_SEP "is" FS_SEP "a" FS_SEP "path"}.string());
+}
+
+TEST(canonPath, requiresAbsolutePath)
+{
+    ASSERT_ANY_THROW(canonPath("."));
+    ASSERT_ANY_THROW(canonPath(".."));
+    ASSERT_ANY_THROW(canonPath("../"));
+    ASSERT_DEATH({ canonPath(""); }, "path != \"\"");
+}
+
+/* ----------------------------------------------------------------------------
+ * dirOf
+ * --------------------------------------------------------------------------*/
+
+TEST(dirOf, returnsEmptyStringForRoot)
+{
+    auto p = dirOf("/");
+
+    ASSERT_EQ(p, "/");
+}
+
+TEST(dirOf, returnsFirstPathComponent)
+{
+    auto p1 = dirOf("/dir/");
+    ASSERT_EQ(p1, "/dir");
+    auto p2 = dirOf("/dir");
+    ASSERT_EQ(p2, "/");
+    auto p3 = dirOf("/dir/..");
+    ASSERT_EQ(p3, "/dir");
+    auto p4 = dirOf("/dir/../");
+    ASSERT_EQ(p4, "/dir/..");
+}
+
+/* ----------------------------------------------------------------------------
+ * baseNameOf
+ * --------------------------------------------------------------------------*/
+
+TEST(baseNameOf, emptyPath)
+{
+    auto p1 = baseNameOf("");
+    ASSERT_EQ(p1, "");
+}
+
+TEST(baseNameOf, pathOnRoot)
+{
+    auto p1 = baseNameOf("/dir");
+    ASSERT_EQ(p1, "dir");
+}
+
+TEST(baseNameOf, relativePath)
+{
+    auto p1 = baseNameOf("dir/foo");
+    ASSERT_EQ(p1, "foo");
+}
+
+TEST(baseNameOf, pathWithTrailingSlashRoot)
+{
+    auto p1 = baseNameOf("/");
+    ASSERT_EQ(p1, "");
+}
+
+TEST(baseNameOf, trailingSlash)
+{
+    auto p1 = baseNameOf("/dir/");
+    ASSERT_EQ(p1, "dir");
+}
+
+TEST(baseNameOf, trailingSlashes)
+{
+    auto p1 = baseNameOf("/dir//");
+    ASSERT_EQ(p1, "dir");
+}
+
+TEST(baseNameOf, absoluteNothingSlashNothing)
+{
+    auto p1 = baseNameOf("//");
+    ASSERT_EQ(p1, "");
+}
+
+/* ----------------------------------------------------------------------------
+ * isInDir
+ * --------------------------------------------------------------------------*/
+
+TEST(isInDir, trivialCase)
+{
+    auto p1 = isInDir("/foo/bar", "/foo");
+    ASSERT_EQ(p1, true);
+}
+
+TEST(isInDir, notInDir)
+{
+    auto p1 = isInDir("/zes/foo/bar", "/foo");
+    ASSERT_EQ(p1, false);
+}
+
+// XXX: hm, bug or feature? :) Looking at the implementation
+// this might be problematic.
+TEST(isInDir, emptyDir)
+{
+    auto p1 = isInDir("/zes/foo/bar", "");
+    ASSERT_EQ(p1, true);
+}
+
+/* ----------------------------------------------------------------------------
+ * isDirOrInDir
+ * --------------------------------------------------------------------------*/
+
+TEST(isDirOrInDir, trueForSameDirectory)
+{
+    ASSERT_EQ(isDirOrInDir("/nix", "/nix"), true);
+    ASSERT_EQ(isDirOrInDir("/", "/"), true);
+}
+
+TEST(isDirOrInDir, trueForEmptyPaths)
+{
+    ASSERT_EQ(isDirOrInDir("", ""), true);
+}
+
+TEST(isDirOrInDir, falseForDisjunctPaths)
+{
+    ASSERT_EQ(isDirOrInDir("/foo", "/bar"), false);
+}
+
+TEST(isDirOrInDir, relativePaths)
+{
+    ASSERT_EQ(isDirOrInDir("/foo/..", "/foo"), true);
+}
+
+// XXX: while it is possible to use "." or ".." in the
+// first argument this doesn't seem to work in the second.
+TEST(isDirOrInDir, DISABLED_shouldWork)
+{
+    ASSERT_EQ(isDirOrInDir("/foo/..", "/foo/."), true);
+}
+
+/* ----------------------------------------------------------------------------
+ * pathExists
+ * --------------------------------------------------------------------------*/
+
+TEST(pathExists, rootExists)
+{
+    ASSERT_TRUE(pathExists(std::filesystem::path{FS_ROOT}.string()));
+}
+
+TEST(pathExists, cwdExists)
+{
+    ASSERT_TRUE(pathExists("."));
+}
+
+TEST(pathExists, bogusPathDoesNotExist)
+{
+    ASSERT_FALSE(pathExists("/schnitzel/darmstadt/pommes"));
+}
+
+/* ----------------------------------------------------------------------------
+ * makeParentCanonical
+ * --------------------------------------------------------------------------*/
+
+TEST(makeParentCanonical, noParent)
+{
+    ASSERT_EQ(makeParentCanonical("file"), absPath(std::filesystem::path("file")));
+}
+
+TEST(makeParentCanonical, root)
+{
+    ASSERT_EQ(makeParentCanonical("/"), "/");
+}
+}