diff --git a/stix2/test/test_observed_data.py b/stix2/test/test_observed_data.py
index a3bff7b..6a56963 100644
--- a/stix2/test/test_observed_data.py
+++ b/stix2/test/test_observed_data.py
@@ -626,7 +626,7 @@ def test_file_example_with_empty_NTFSExt():
                    })
 
     assert excinfo.value.cls == stix2.NTFSExt
-    assert excinfo.value.fields == sorted(list(stix2.NTFSExt._properties.keys()))
+    assert excinfo.value.properties == sorted(list(stix2.NTFSExt._properties.keys()))
 
 
 def test_file_example_with_PDFExt():
@@ -871,7 +871,7 @@ def test_mutex_example():
 
 
 def test_process_example():
-    p = stix2.Process(_valid_refs=["0"],
+    p = stix2.Process(_valid_refs={"0": "file"},
                       pid=1221,
                       name="gedit-bin",
                       created="2016-01-20T14:11:25.55Z",
@@ -889,7 +889,7 @@ def test_process_example_empty_error():
     assert excinfo.value.cls == stix2.Process
     properties_of_process = list(stix2.Process._properties.keys())
     properties_of_process.remove("type")
-    assert excinfo.value.fields == sorted(properties_of_process)
+    assert excinfo.value.properties == sorted(properties_of_process)
 
 
 def test_process_example_empty_with_extensions():
@@ -900,7 +900,7 @@ def test_process_example_empty_with_extensions():
 
     assert excinfo.value.cls == stix2.WindowsProcessExt
     properties_of_extension = list(stix2.WindowsProcessExt._properties.keys())
-    assert excinfo.value.fields == sorted(properties_of_extension)
+    assert excinfo.value.properties == sorted(properties_of_extension)
 
 
 def test_process_example_windows_process_ext_empty():
@@ -913,7 +913,7 @@ def test_process_example_windows_process_ext_empty():
 
     assert excinfo.value.cls == stix2.WindowsProcessExt
     properties_of_extension = list(stix2.WindowsProcessExt._properties.keys())
-    assert excinfo.value.fields == sorted(properties_of_extension)
+    assert excinfo.value.properties == sorted(properties_of_extension)
 
 
 def test_process_example_extensions_empty():
@@ -924,7 +924,7 @@ def test_process_example_extensions_empty():
     assert excinfo.value.cls == stix2.Process
     properties_of_process = list(stix2.Process._properties.keys())
     properties_of_process.remove("type")
-    assert excinfo.value.fields == sorted(properties_of_process)
+    assert excinfo.value.properties == sorted(properties_of_process)
 
 
 def test_process_example_with_WindowsProcessExt_Object():
diff --git a/stix2/test/test_properties.py b/stix2/test/test_properties.py
index 5dc0084..59e0dd9 100644
--- a/stix2/test/test_properties.py
+++ b/stix2/test/test_properties.py
@@ -1,7 +1,7 @@
 import pytest
 
 from stix2 import TCPExt
-from stix2.exceptions import DictionaryKeyError
+from stix2.exceptions import AtLeastOnePropertyError, DictionaryKeyError
 from stix2.observables import EmailMIMEComponent
 from stix2.properties import (BinaryProperty, BooleanProperty,
                               DictionaryProperty, EmbeddedObjectProperty,
@@ -272,7 +272,6 @@ def test_extension_property_valid():
     {'foobar-ext': {
         'pe_type': 'exe'
     }},
-    {'windows-pebinary-ext': TCPExt()},
 ])
 def test_extension_property_invalid(data):
     ext_prop = ExtensionsProperty(enclosing_type='file')
@@ -289,3 +288,8 @@ def test_extension_property_invalid_type():
             }}
         )
     assert 'no extensions defined' in str(excinfo.value)
+
+
+def test_extension_at_least_one_property_constraint():
+    with pytest.raises(AtLeastOnePropertyError):
+        TCPExt()