os, filepath: reorganize functions

vlib/filepath/filepath_test.v

@@ -0,0 +1,43 @@
+import filepath
+
+fn test_ext() {
+	assert filepath.ext('file.v') == '.v'
+	assert filepath.ext('file') == ''
+}
+
+fn test_is_abs() {
+	assert filepath.is_abs('/home/user') == true
+	assert filepath.is_abs('v/vlib') == false
+
+	$if windows {
+		assert filepath.is_abs('C:\\Windows\\') == true
+	}
+}
+
+fn test_join() {
+	$if windows {
+		assert filepath.join('v', 'vlib', 'filepath') == 'v\\vlib\\filepath'
+	} $else {
+		assert filepath.join('v', 'vlib', 'filepath') == 'v/vlib/filepath'
+	}
+}
+
+fn test_dir() {
+	$if windows {
+		assert filepath.dir('C:\\a\\b\\c') == 'C:\\a\\b'
+	} $else {
+		assert filepath.dir('/var/tmp/foo') == '/var/tmp'
+	}
+
+	assert filepath.dir('filepath') == '.'
+}
+
+fn test_basedir() {
+	$if windows {
+		assert filepath.basedir('v\\vlib\\filepath') == 'v\\vlib'
+	} $else {
+		assert filepath.basedir('v/vlib/filepath') == 'v/vlib'
+	}
+
+	assert filepath.basedir('filename') == 'filename'
+}