test(expand): Add some tests for expand (#1505)

tests/fixtures/expand/with-spaces.txt

@@ -0,0 +1,6 @@
+// !note: file contains significant whitespace
+// * indentation uses <SPACE> characters
+int foo() {
+    // with spaces
+    return 0;
+}

tests/fixtures/expand/with-tab.txt

@@ -0,0 +1,6 @@
+// !note: file contains significant whitespace
+// * indentation uses <TAB> characters
+int main() {
+	// with tabs
+	return 0;
+}

tests/fixtures/expand/with-trailing-tab.txt

@@ -0,0 +1,7 @@
+// !note: file contains significant whitespace
+// * indentation uses <TAB> characters
+int main() {
+	// * next line has both a leading & trailing tab
+	// with tabs=>	
+	return 0;
+}