Add unit tests for Cvar::Modified

Note: previously I was thinking that I would need a Modified latched
cvar so there are a bunch of tests for that case. But we may end up not
using it.

Author: slipher

src.cmake

@@ -90,6 +90,7 @@ endif()
 set(COMMONTESTLIST
     ${LIB_DIR}/tinyformat/TinyformatTest.cpp
     ${COMMON_DIR}/ColorTest.cpp
+    ${COMMON_DIR}/CvarTest.cpp
     ${COMMON_DIR}/FileSystemTest.cpp
     ${COMMON_DIR}/StringTest.cpp
     ${COMMON_DIR}/cm/unittest.cpp

src/common/CvarTest.cpp

@@ -0,0 +1,94 @@
+/*
+===========================================================================
+Daemon BSD Source Code
+Copyright (c) 2024, Daemon Developers
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+* Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+* Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions and the following disclaimer in the
+documentation and/or other materials provided with the distribution.
+* Neither the name of the Daemon developers nor the
+names of its contributors may be used to endorse or promote products
+derived from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL DAEMON DEVELOPERS BE LIABLE FOR ANY
+DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+===========================================================================
+*/
+
+#include <gtest/gtest.h>
+
+#include "common/Common.h"
+#include "engine/framework/CvarSystem.h"
+
+namespace Cvar {
+namespace {
+
+TEST(ModifiedCvarTest, Normal)
+{
+    Modified<Cvar<int>> cv("test_modified", "desc", NONE, 3);
+    Util::optional<int> modified = cv.GetModifiedValue();
+    ASSERT_TRUE(modified); // modified flag is true on birth
+    ASSERT_EQ(modified.value(), 3);
+
+    // now cleared
+    ASSERT_FALSE(cv.GetModifiedValue());
+    ASSERT_FALSE(cv.GetModifiedValue());
+
+    // test setting via the cvar object
+    cv.Set(9);
+    modified = cv.GetModifiedValue();
+    ASSERT_TRUE(modified);
+    ASSERT_EQ(modified.value(), 9);
+
+    ASSERT_FALSE(cv.GetModifiedValue());
+
+    // test setting externally
+    SetValue("test_modified", "1");
+    modified = cv.GetModifiedValue();
+    ASSERT_TRUE(modified);
+    ASSERT_EQ(modified.value(), 1);
+
+    ASSERT_FALSE(cv.GetModifiedValue());
+
+    // test that invalid set is ignored
+    SetValue("test_modified", "a");
+    ASSERT_FALSE(cv.GetModifiedValue());
+}
+
+TEST(ModifiedCvarTest, Latch)
+{
+    Modified<Cvar<float>> cv("test_modifiedLatched", "desc", NONE, 1.5f);
+    Latch(cv);
+    ASSERT_TRUE(cv.GetModifiedValue());
+    ASSERT_FALSE(cv.GetModifiedValue());
+
+    cv.Set(-5.0f);
+    ASSERT_EQ(cv.Get(), 1.5f);
+
+    // Clear latch flag. It's probably true now because the implementation of latched cvars
+    // sets them to the new value and back to the current value, but let's not make this
+    // part of the contract.
+    cv.GetModifiedValue();
+
+    // Make sure modified flag is set upon unlatching
+    Latch(cv);
+    Util::optional<float> modified = cv.GetModifiedValue();
+    ASSERT_TRUE(modified);
+    ASSERT_EQ(modified.value(), -5.0f);
+}
+
+} // namespace Cvar
+} // namespace