Fix TestConfigurationMgr to have correct expectations.

Author: bzbarsky-apple

src/platform/tests/TestConfigurationMgr.cpp

@@ -389,10 +389,17 @@ TEST_F(TestConfigurationMgr, GetPrimaryMACAddress)
     MutableByteSpan mac6Bytes(macBuffer6Bytes);
 
     err = ConfigurationMgr().GetPrimaryMACAddress(mac8Bytes);
-    if (mac8Bytes.size() != ConfigurationManager::kPrimaryMACAddressLength)
+    if (sizeof(macBuffer8Bytes) != ConfigurationManager::kPrimaryMACAddressLength)
     {
+        // Should have failed input validation
         EXPECT_EQ(err, CHIP_ERROR_INVALID_ARGUMENT);
     }
+    else if (mac8Bytes.size() != ConfigurationManager::kPrimaryMACAddressLength)
+    {
+        // This can happen if the primary address is Thread but then there is no
+        // Thread address to be had and we fell back to Wi-Fi.
+        EXPECT_EQ(mac8Bytes.size(), ConfigurationManager::kEthernetMACAddressLength);
+    }
 
     err = ConfigurationMgr().GetPrimaryMACAddress(mac6Bytes);
     if (mac6Bytes.size() != ConfigurationManager::kPrimaryMACAddressLength)