MXS-2218 Add simple housekeeper test

So that the new worker based housekeeper can be tested.

server/core/test/CMakeLists.txt

@@ -7,6 +7,7 @@ add_executable(test_dcb test_dcb.cc)
 add_executable(test_event test_event.cc)
 add_executable(test_filter test_filter.cc)
 add_executable(test_hint test_hint.cc)
+add_executable(test_housekeeper test_housekeeper.cc)
 add_executable(test_http test_http.cc)
 add_executable(test_json test_json.cc)
 add_executable(test_local_address test_local_address.cc)
@@ -34,6 +35,7 @@ target_link_libraries(test_dcb maxscale-common)
 target_link_libraries(test_event maxscale-common)
 target_link_libraries(test_filter maxscale-common)
 target_link_libraries(test_hint maxscale-common)
+target_link_libraries(test_housekeeper maxscale-common)
 target_link_libraries(test_http maxscale-common)
 target_link_libraries(test_json maxscale-common)
 target_link_libraries(test_local_address maxscale-common)
@@ -60,6 +62,7 @@ add_test(test_dcb test_dcb)
 add_test(test_event test_event)
 add_test(test_filter test_filter)
 add_test(test_hint test_hint)
+add_test(test_housekeeper test_housekeeper)
 add_test(test_http test_http)
 add_test(test_json test_json)
 add_test(test_log test_log)

server/core/test/test_housekeeper.cc

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2022-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <atomic>
+#include <iostream>
+#include <maxbase/log.hh>
+#include <maxscale/housekeeper.h>
+#include "test_utils.hh"
+
+using namespace std;
+
+namespace
+{
+
+std::atomic<int> n_oneshot;
+std::atomic<int> n_repeating;
+
+const char* ZONESHOT_NAME   = "OneShot";
+const char* ZREPEATING_NAME = "Repeating";
+
+bool oneshot(void*)
+{
+    ++n_oneshot;
+    return false; // Remove from housekeeper.
+}
+
+bool repeating(void*)
+{
+    ++n_repeating;
+    return true; // Continue calling.
+}
+
+int test()
+{
+    int rc = EXIT_SUCCESS;
+
+    hktask_add(ZONESHOT_NAME, oneshot, nullptr, 1); // Call oneshot, once per second.
+    hktask_add(ZREPEATING_NAME, repeating, nullptr, 1); // Call repeating, once per second.
+
+    sleep(4); // Should get 1 oneshot call and ~4 repeating calls.
+
+    hktask_remove(ZREPEATING_NAME);
+
+    int n;
+
+    n = n_oneshot.load();
+    cout << "Oneshots: " << n << endl;
+
+    if (n != 1)
+    {
+        cerr << "Expected 1 oneshots, got " << n << "." << endl;
+        rc = EXIT_FAILURE;
+    }
+
+    n = n_repeating.load();
+    cout << "Repeating: " << n << endl;
+
+    // Let's check that the task removal really had an effect.
+    sleep(2);
+
+    if (n != n_repeating.load())
+    {
+        cerr << "Removed task was called." << endl;
+        rc = EXIT_FAILURE;
+    }
+
+    // Timing involved, so we allow for some non-determinism.
+    if (n < 3 || n > 5)
+    {
+        cerr << "Expected ~4 repeating, got " << n << "." << endl;
+        rc = EXIT_FAILURE;
+    }
+
+    return rc;
+}
+
+}
+
+int main(int argc, char** argv)
+{
+    int rc = EXIT_FAILURE;
+
+    init_test_env();
+
+    if (hkinit())
+    {
+        if (hkstart())
+        {
+            rc = test();
+        }
+        else
+        {
+            cerr << "Could not start the housekeeper." << endl;
+        }
+
+        hkfinish();
+    }
+    else
+    {
+        cerr << "Could not initialize the housekeeper." << endl;
+    }
+
+    return rc;
+}