diff --git a/mfbatch/commands.py b/mfbatch/commands.py
index 0b5574b..4da9ea9 100644
--- a/mfbatch/commands.py
+++ b/mfbatch/commands.py
@@ -11,7 +11,7 @@ import os.path
 
 from typing import Dict, Tuple, Optional
 
-import mfbatch.metaflac as flac
+from mfbatch.metaflac import write_metadata as flac 
 
 
 class UnrecognizedCommandError(Exception):
@@ -158,6 +158,7 @@ they appear in the batchfile.
     def __init__(self):
         self.dry_run = True
         self.env = CommandEnv()
+        self.write_metadata_f = flac
 
     def eval(self, line: str, lineno: int, interactive: bool):
         """
@@ -192,7 +193,7 @@ they appear in the batchfile.
             print("DRY RUN would write metadata here.")
         else:
             sys.stdout.write("Writing metadata... ")
-            flac.write_metadata(line, self.env.metadatums)
+            self.write_metadata_f(line, self.env.metadatums)
             sys.stdout.write("Complete!")
 
         self.env.increment_all()
diff --git a/tests/__init__.py b/tests/__init__.py
index 559c360..2436f75 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -1,19 +1,36 @@
 "mfbatch tests"
 
 import unittest
+from unittest.mock import MagicMock
+from typing import cast
 
-from mfbatch.commands import BatchfileParser 
+from mfbatch.commands import BatchfileParser
 
 class CommandTests(unittest.TestCase):
     def setUp(self):
         self.command_parser = BatchfileParser()
+        self.command_parser.dry_run = False
+        self.command_parser.write_metadata_f = MagicMock()       
 
     def tearDown(self):
         pass
 
+    def testSetWithoutWrite(self):
+        self.command_parser.set(['TYPE', 'Everything'])
+        self.assertFalse(cast(MagicMock, 
+                             self.command_parser.write_metadata_f).called)
+        self.assertEqual(self.command_parser.env.metadatums['TYPE'],
+                         'Everything')
+
     def testSetCommand(self):
         self.command_parser.set(['X', 'Y'])
-        self.assertEqual(self.command_parser.env.metadatums['X'], 'Y')
+        self.command_parser.eval("./testfile.flac", lineno=1,
+                                 interactive=False)
+        self.assertTrue(cast(MagicMock, 
+                             self.command_parser.write_metadata_f).called)
+        self.assertEqual(cast(MagicMock, 
+                             self.command_parser.write_metadata_f).call_args.args,
+                         ('./testfile.flac', {'X': 'Y'}))
 
     def testUnsetCommand(self):
         self.command_parser.set(['A', '1'])