diff --git a/tests/bhyvexml2xmltest.c b/tests/bhyvexml2xmltest.c
index d860a41..2d34a00 100644
--- a/tests/bhyvexml2xmltest.c
+++ b/tests/bhyvexml2xmltest.c
@@ -32,7 +32,8 @@ testCompareXMLToXMLHelper(const void *data)
 
     ret = testCompareDomXML2XMLFiles(driver.caps, driver.xmlopt, xml_in,
                                      info->different ? xml_out : xml_in,
-                                     false);
+                                     false,
+                                     NULL, NULL);
 
  cleanup:
     VIR_FREE(xml_in);
diff --git a/tests/genericxml2xmltest.c b/tests/genericxml2xmltest.c
index 7f79896..aa3a570 100644
--- a/tests/genericxml2xmltest.c
+++ b/tests/genericxml2xmltest.c
@@ -39,7 +39,8 @@ testCompareXMLToXMLHelper(const void *data)
 
     ret = testCompareDomXML2XMLFiles(caps, xmlopt, xml_in,
                                      info->different ? xml_out : xml_in,
-                                     !info->inactive_only);
+                                     !info->inactive_only,
+                                     NULL, NULL);
  cleanup:
     VIR_FREE(xml_in);
     VIR_FREE(xml_out);
diff --git a/tests/lxcxml2xmltest.c b/tests/lxcxml2xmltest.c
index e460d0a..aafebb4 100644
--- a/tests/lxcxml2xmltest.c
+++ b/tests/lxcxml2xmltest.c
@@ -44,7 +44,8 @@ testCompareXMLToXMLHelper(const void *data)
 
     ret = testCompareDomXML2XMLFiles(caps, xmlopt, xml_in,
                                      info->different ? xml_out : xml_in,
-                                     !info->inactive_only);
+                                     !info->inactive_only,
+                                     NULL, NULL);
  cleanup:
     VIR_FREE(xml_in);
     VIR_FREE(xml_out);
diff --git a/tests/qemuxml2xmltest.c b/tests/qemuxml2xmltest.c
index 0134815..97838f3 100644
--- a/tests/qemuxml2xmltest.c
+++ b/tests/qemuxml2xmltest.c
@@ -42,7 +42,8 @@ testXML2XMLActive(const void *opaque)
     const struct testInfo *info = opaque;
 
     return testCompareDomXML2XMLFiles(driver.caps, driver.xmlopt,
-                                      info->inName, info->outActiveName, true);
+                                      info->inName, info->outActiveName, true,
+                                      NULL, NULL);
 }
 
 
@@ -52,7 +53,8 @@ testXML2XMLInactive(const void *opaque)
     const struct testInfo *info = opaque;
 
     return testCompareDomXML2XMLFiles(driver.caps, driver.xmlopt, info->inName,
-                                      info->outInactiveName, false);
+                                      info->outInactiveName, false,
+                                      NULL, NULL);
 }
 
 
diff --git a/tests/testutils.c b/tests/testutils.c
index 10c26648..c282745 100644
--- a/tests/testutils.c
+++ b/tests/testutils.c
@@ -1097,7 +1097,9 @@ virDomainXMLOptionPtr virTestGenericDomainXMLConfInit(void)
 
 int
 testCompareDomXML2XMLFiles(virCapsPtr caps, virDomainXMLOptionPtr xmlopt,
-                           const char *infile, const char *outfile, bool live)
+                           const char *infile, const char *outfile, bool live,
+                           testCompareDomXML2XMLPreFormatCallback cb,
+                           const void *opaque)
 {
     char *actual = NULL;
     int ret = -1;
@@ -1115,6 +1117,9 @@ testCompareDomXML2XMLFiles(virCapsPtr caps, virDomainXMLOptionPtr xmlopt,
         goto fail;
     }
 
+    if (cb && cb(def, opaque) < 0)
+        goto fail;
+
     if (!(actual = virDomainDefFormat(def, format_flags)))
         goto fail;
 
diff --git a/tests/testutils.h b/tests/testutils.h
index b1d7397..df2b2a6 100644
--- a/tests/testutils.h
+++ b/tests/testutils.h
@@ -137,10 +137,14 @@ int virtTestMain(int argc,
 virCapsPtr virTestGenericCapsInit(void);
 virDomainXMLOptionPtr virTestGenericDomainXMLConfInit(void);
 
+typedef int (*testCompareDomXML2XMLPreFormatCallback)(virDomainDefPtr def,
+                                                      const void *opaque);
 int testCompareDomXML2XMLFiles(virCapsPtr caps,
                                virDomainXMLOptionPtr xmlopt,
                                const char *inxml,
                                const char *outfile,
-                               bool live);
+                               bool live,
+                               testCompareDomXML2XMLPreFormatCallback cb,
+                               const void *opaque);
 
 #endif /* __VIT_TEST_UTILS_H__ */
