Fixed FileCacheTest.CleanCacheTest

All FileCacheTest unit tests now passing.
  - 4 HashedFileCacheTest unit tests still failing.

FileCacheManager was missing the DateTime version of `WriteSysValue()`.
Added it to achieve function parity with `ReadSysValue()` functions.

src/FileCache.UnitTests/FileCache.UnitTests.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net452;netcoreapp5.0</TargetFrameworks>
+    <TargetFrameworks>netcoreapp5.0</TargetFrameworks>
     <IsPackable>false</IsPackable>
     <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects>
     <GenerateBindingRedirectsOutputType>true</GenerateBindingRedirectsOutputType>

src/FileCache/FileCache.cs

@@ -692,8 +692,9 @@ public void Flush(DateTime minDate, string regionName = null)
                         string policyPath = CacheManager.GetPolicyPath(key, region);
                         string cachePath = CacheManager.GetCachePath(key, region);
 
-                        // Update the Cache size
+                        // Update the Cache size before flushing this item.
                         CurrentCacheSize = GetCacheSize();
+
                         //if either policy or cache are stale, delete both
                         if (File.GetLastAccessTime(policyPath) < minDate || File.GetLastAccessTime(cachePath) < minDate)
                         {
@@ -706,6 +707,7 @@ public void Flush(DateTime minDate, string regionName = null)
                 cLock.Close();
             }
         }
+
         /// <summary>
         /// Returns the policy attached to a given cache item.
         /// </summary>

src/FileCache/FileCacheManager.cs

@@ -488,6 +488,18 @@ public void WriteSysValue(string filename, long data)
             }
         }
 
+        /// <summary>
+        /// Writes a long to a system file that is not part of the cache itself,
+        /// but is used to help it function.
+        /// </summary>
+        /// <param name="filename">The name of the sysfile (without directory)</param>
+        /// <param name="data">The DateTime to write to the file</param>
+        public void WriteSysValue(string filename, DateTime data)
+        {
+            // Convert to long and use long's function.
+            WriteSysValue(filename, data.ToBinary());
+        }
+
         /// <summary>
         /// This function servies to centralize file stream access within this class.
         /// </summary>