Bug fixes and unit tests (#14)

Added unit tests for I2C_eeprom_cyclic_store and fixed a bug in the format() method and a possible bug with the "empty" marker literal being expressed as ~0UL (which isn't necessarily the same size as a uint32_t).

I2C_eeprom_cyclic_store.h

@@ -75,18 +75,25 @@ public:
       * 
       * Formatting is done by writing the max version number to each slot,
       * thus it performs a write cycle to the first write page of each slot. 
+      *
+      * @return True if successful or false if unable to write to eeprom.
       */
-    void format()
+    bool format()
     {
         // Reset the EEPROM by writing a ~0 into all pages
-        for (uint16_t slot = 0; slot < _totalPages; slot++)
+        auto totalSlots = _totalPages / _bufferPages;
+        auto slotSize = _pageSize * _bufferPages;
+        for (uint16_t slot = 0; slot < totalSlots; slot++)
         {
-            _eeprom->writeBlock(slot * _pageSize, (uint8_t *)"\xff\xff\xff\xff", 4);
+            if(_eeprom->writeBlock(slot * slotSize, (uint8_t *)"\xff\xff\xff\xff", 4) != 0)
+                return false;
         }
 
         _isEmpty = true;
         _currentSlot = 0;
         _isInitialized = true;
+
+	return true;
     }
 
     /**
@@ -219,7 +226,7 @@ private:
             return false;
         }
 
-        if (current == ~0UL)
+        if (current == 0xffffffff)
         {
             // Memory is blank
             _isEmpty = true;
@@ -236,7 +243,7 @@ private:
                 return false;
             }
 
-            if (probe == ~0UL || probe <= current)
+            if (probe == 0xffffffff || probe <= current)
             {
                 // 1. Nothing has been written to the memory at Probe
                 // 2. The slots have the same timestamp, this shouldn't happen, treat as if Probe slot hasn't been written