diff --git a/test/unit/os_unix.moon b/test/unit/os_unix.moon
new file mode 100644
index 0000000000..2e817673a4
--- /dev/null
+++ b/test/unit/os_unix.moon
@@ -0,0 +1,40 @@
+{:cimport, :eq, :ffi} = require 'test.unit.helpers'
+
+cstr = ffi.typeof 'char[?]'
+os = cimport './src/os_unix.h'
+
+describe 'os_unix function', ->
+  describe 'mch_isdir', ->
+    TRUE = 1
+    FALSE = 0
+
+    ffi.cdef('int mch_isdir(char * name);')
+
+    mch_isdir = (name) ->
+      name = cstr (string.len name), name
+      os.mch_isdir(name)
+
+    setup ->
+      lfs.mkdir 'empty-test-directory'
+      lfs.touch 'empty-test-directory/test.file'
+
+    teardown ->
+      lfs.rmdir 'empty-test-directory'
+
+    it 'returns false if an empty string is given', ->
+      eq FALSE, (mch_isdir '')
+
+    it 'returns false if a nonexisting directory is given', ->
+      eq FALSE, (mch_isdir 'non-existing-directory')
+
+    it 'returns false if an existing file is given', ->
+      eq FALSE, (mch_isdir 'non-existing-directory/test.file')
+
+    it 'returns true if the current directory is given', ->
+      eq TRUE, (mch_isdir '.')
+
+    it 'returns true if the parent directory is given', ->
+      eq TRUE, (mch_isdir '..')
+
+    it 'returns true if an newly created directory is given', ->
+      eq TRUE, (mch_isdir 'empty-test-directory')