Updated test case documentation

docs/test_cases/t20027.md

@@ -0,0 +1,48 @@
+# t20027 - Filter call expressions based on access test case
+## Config
+```yaml
+compilation_database_dir: ..
+output_directory: puml
+diagrams:
+  t20027_sequence:
+    type: sequence
+    glob:
+      - ../../tests/t20027/t20027.cc
+    include:
+      namespaces:
+        - clanguml::t20027
+      access:
+        - public
+    using_namespace:
+      - clanguml::t20027
+    start_from:
+      - function: "clanguml::t20027::tmain()"
+```
+## Source code
+File t20027.cc
+```cpp
+namespace clanguml {
+namespace t20027 {
+
+class A {
+public:
+    void a() { aa(); }
+
+protected:
+    void aa() { aaa(); }
+
+private:
+    void aaa() { }
+};
+
+void tmain()
+{
+    A a;
+
+    a.a();
+}
+}
+}
+```
+## Generated UML diagrams
+![t20027_sequence](./t20027_sequence.svg "Filter call expressions based on access test case")