optional preview frame

tests/RenderCadenceCompositorPreviewConfigTests.cpp

@@ -0,0 +1,50 @@
+#include "PreviewConfig.h"
+
+#include <iostream>
+
+namespace
+{
+int gFailures = 0;
+
+void Expect(bool condition, const char* message)
+{
+	if (condition)
+		return;
+
+	std::cerr << "FAIL: " << message << "\n";
+	++gFailures;
+}
+
+void TestTimerIntervalUsesConfiguredFps()
+{
+	Expect(RenderCadenceCompositor::PreviewTimerIntervalMilliseconds(25.0) == 40, "25 fps maps to 40 ms");
+	Expect(RenderCadenceCompositor::PreviewTimerIntervalMilliseconds(50.0) == 20, "50 fps maps to 20 ms");
+}
+
+void TestInvalidFpsUsesDefault()
+{
+	Expect(
+		RenderCadenceCompositor::PreviewTimerIntervalMilliseconds(0.0) ==
+			RenderCadenceCompositor::PreviewTimerIntervalMilliseconds(RenderCadenceCompositor::kDefaultPreviewFps),
+		"zero preview fps uses default interval");
+	Expect(
+		RenderCadenceCompositor::PreviewTimerIntervalMilliseconds(-10.0) ==
+			RenderCadenceCompositor::PreviewTimerIntervalMilliseconds(RenderCadenceCompositor::kDefaultPreviewFps),
+		"negative preview fps uses default interval");
+}
+}
+
+int main()
+{
+	TestTimerIntervalUsesConfiguredFps();
+	TestInvalidFpsUsesDefault();
+
+	if (gFailures != 0)
+	{
+		std::cerr << gFailures << " preview config test failure(s).\n";
+		return 1;
+	}
+
+	std::cout << "RenderCadenceCompositor preview config tests passed.\n";
+	return 0;
+}