cleanup: Map test files according to structure in src

For example cmd_account() is located in src/command/cmd_funcs.c.
The unit test was located in tests/unittests/test_cmd_account.c.
Let's move it to a subdirectory like tests/unittests/command/test_cmd_account.c
to correpsond to the same structure.

tests/unittests/xmpp/test_chat_session.c

@@ -0,0 +1,52 @@
+#include <string.h>
+#include "prof_cmocka.h"
+#include <stdlib.h>
+
+#include "xmpp/chat_session.h"
+
+void
+returns_false_when_chat_session_does_not_exist(void** state)
+{
+    ChatSession* session = chat_session_get("somejid@server.org");
+    assert_null(session);
+}
+
+void
+creates_chat_session_on_recipient_activity(void** state)
+{
+    char* barejid = "myjid@server.org";
+    char* resource = "tablet";
+
+    chat_session_recipient_active(barejid, resource, FALSE);
+    ChatSession* session = chat_session_get(barejid);
+
+    assert_non_null(session);
+    assert_string_equal(session->resource, resource);
+}
+
+void
+replaces_chat_session_on_recipient_activity_with_different_resource(void** state)
+{
+    char* barejid = "myjid@server.org";
+    char* resource1 = "tablet";
+    char* resource2 = "mobile";
+
+    chat_session_recipient_active(barejid, resource1, FALSE);
+    chat_session_recipient_active(barejid, resource2, FALSE);
+    ChatSession* session = chat_session_get(barejid);
+
+    assert_string_equal(session->resource, resource2);
+}
+
+void
+removes_chat_session(void** state)
+{
+    char* barejid = "myjid@server.org";
+    char* resource1 = "laptop";
+
+    chat_session_recipient_active(barejid, resource1, FALSE);
+    chat_session_remove(barejid);
+    ChatSession* session = chat_session_get(barejid);
+
+    assert_null(session);
+}