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/command/test_cmd_sub.c

@@ -0,0 +1,39 @@
+#include "prof_cmocka.h"
+#include <stdlib.h>
+#include <string.h>
+#include <glib.h>
+
+#include "xmpp/xmpp.h"
+
+#include "ui/ui.h"
+#include "ui/stub_ui.h"
+
+#include "command/cmd_funcs.h"
+
+#define CMD_SUB "/sub"
+
+void
+cmd_sub_shows_message_when_not_connected(void** state)
+{
+    gchar* args[] = { NULL };
+
+    will_return(connection_get_status, JABBER_DISCONNECTED);
+
+    expect_cons_show("You are currently not connected.");
+
+    gboolean result = cmd_sub(NULL, CMD_SUB, args);
+    assert_true(result);
+}
+
+void
+cmd_sub_shows_usage_when_no_arg(void** state)
+{
+    gchar* args[] = { NULL };
+
+    will_return(connection_get_status, JABBER_CONNECTED);
+
+    expect_string(cons_bad_cmd_usage, cmd, CMD_SUB);
+
+    gboolean result = cmd_sub(NULL, CMD_SUB, args);
+    assert_true(result);
+}