Check for required args first, and check for them all at once.

This is necessary for versions of Python <3.6, where dictionaries are
unordered by default, meaning we can't ensure the order in which fields
are checked.

README.md

@@ -61,7 +61,7 @@ will result in an error:
 
 ```python
 >>> indicator = Indicator()
-ValueError: Missing required field for Indicator: 'labels'
+ValueError: Missing required field(s) for Indicator: (labels, pattern).
 ```
 
 However, the required `valid_from` attribute on Indicators will be set to the

stix2/__init__.py

@@ -74,12 +74,15 @@ class _STIXBase(collections.Mapping):
         if extra_kwargs:
             raise TypeError("unexpected keyword arguments: " + str(extra_kwargs))
 
+        required_fields = [k for k, v in cls._properties.items() if v.get('required')]
+        missing_kwargs = set(required_fields) - set(kwargs)
+        if missing_kwargs:
+            msg = "Missing required field(s) for {type}: ({fields})."
+            field_list = ", ".join(x for x in sorted(list(missing_kwargs)))
+            raise ValueError(msg.format(type=class_name, fields=field_list))
+
         for prop_name, prop_metadata in cls._properties.items():
             if prop_name not in kwargs:
-                if prop_metadata.get('required'):
-                    msg = "Missing required field for {type}: '{field}'."
-                    raise ValueError(msg.format(type=class_name,
-                                                field=prop_name))
                 if prop_metadata.get('default'):
                     default = prop_metadata['default']
                     if default == NOW:

stix2/test/test_stix2.py

@@ -150,29 +150,28 @@ def test_indicator_autogenerated_fields(indicator):
 
 def test_indicator_type_must_be_indicator():
     with pytest.raises(ValueError) as excinfo:
-        indicator = stix2.Indicator(type='xxx')
+        indicator = stix2.Indicator(type='xxx', **INDICATOR_KWARGS)
 
     assert "Indicator must have type='indicator'." in str(excinfo)
 
 
 def test_indicator_id_must_start_with_indicator():
     with pytest.raises(ValueError) as excinfo:
-        indicator = stix2.Indicator(id='my-prefix--')
+        indicator = stix2.Indicator(id='my-prefix--', **INDICATOR_KWARGS)
 
     assert "Indicator id values must begin with 'indicator--'." in str(excinfo)
 
 
-def test_indicator_required_field_labels():
+def test_indicator_required_fields():
     with pytest.raises(ValueError) as excinfo:
         indicator = stix2.Indicator()
-    assert "Missing required field for Indicator: 'labels'." in str(excinfo)
+    assert "Missing required field(s) for Indicator: (labels, pattern)." in str(excinfo)
 
 
 def test_indicator_required_field_pattern():
     with pytest.raises(ValueError) as excinfo:
-        # Label is checked first, so make sure that is provided
         indicator = stix2.Indicator(labels=['malicious-activity'])
-    assert "Missing required field for Indicator: 'pattern'." in str(excinfo)
+    assert "Missing required field(s) for Indicator: (pattern)." in str(excinfo)
 
 
 def test_cannot_assign_to_indicator_attributes(indicator):
@@ -240,29 +239,28 @@ def test_malware_autogenerated_fields(malware):
 
 def test_malware_type_must_be_malware():
     with pytest.raises(ValueError) as excinfo:
-        malware = stix2.Malware(type='xxx')
+        malware = stix2.Malware(type='xxx', **MALWARE_KWARGS)
 
     assert "Malware must have type='malware'." in str(excinfo)
 
 
 def test_malware_id_must_start_with_malware():
     with pytest.raises(ValueError) as excinfo:
-        malware = stix2.Malware(id='my-prefix--')
+        malware = stix2.Malware(id='my-prefix--', **MALWARE_KWARGS)
 
     assert "Malware id values must begin with 'malware--'." in str(excinfo)
 
 
-def test_malware_required_field_labels():
+def test_malware_required_fields():
     with pytest.raises(ValueError) as excinfo:
         malware = stix2.Malware()
-    assert "Missing required field for Malware: 'labels'." in str(excinfo)
+    assert "Missing required field(s) for Malware: (labels, name)." in str(excinfo)
 
 
 def test_malware_required_field_name():
     with pytest.raises(ValueError) as excinfo:
-        # Label is checked first, so make sure that is provided
         malware = stix2.Malware(labels=['ransomware'])
-    assert "Missing required field for Malware: 'name'." in str(excinfo)
+    assert "Missing required field(s) for Malware: (name)." in str(excinfo)
 
 
 def test_cannot_assign_to_malware_attributes(malware):
@@ -324,14 +322,14 @@ def test_relationship_autogenerated_fields(relationship):
 
 def test_relationship_type_must_be_relationship():
     with pytest.raises(ValueError) as excinfo:
-        relationship = stix2.Relationship(type='xxx')
+        relationship = stix2.Relationship(type='xxx', **RELATIONSHIP_KWARGS)
 
     assert "Relationship must have type='relationship'." in str(excinfo)
 
 
 def test_relationship_id_must_start_with_relationship():
     with pytest.raises(ValueError) as excinfo:
-        relationship = stix2.Relationship(id='my-prefix--')
+        relationship = stix2.Relationship(id='my-prefix--', **RELATIONSHIP_KWARGS)
 
     assert "Relationship id values must begin with 'relationship--'." in str(excinfo)
 
@@ -339,24 +337,23 @@ def test_relationship_id_must_start_with_relationship():
 def test_relationship_required_field_relationship_type():
     with pytest.raises(ValueError) as excinfo:
         relationship = stix2.Relationship()
-    assert "Missing required field for Relationship: 'relationship_type'." in str(excinfo)
+    assert "Missing required field(s) for Relationship: (relationship_type, source_ref, target_ref)." in str(excinfo)
 
 
-def test_relationship_required_field_source_ref():
+def test_relationship_missing_some_required_fields():
     with pytest.raises(ValueError) as excinfo:
         # relationship_type is checked first, so make sure that is provided
         relationship = stix2.Relationship(relationship_type='indicates')
-    assert "Missing required field for Relationship: 'source_ref'." in str(excinfo)
+    assert "Missing required field(s) for Relationship: (source_ref, target_ref)." in str(excinfo)
 
 
 def test_relationship_required_field_target_ref():
     with pytest.raises(ValueError) as excinfo:
-        # relationship_type and source_ref are checked first, so make sure those are provided
         relationship = stix2.Relationship(
             relationship_type='indicates',
             source_ref=INDICATOR_ID
         )
-    assert "Missing required field for Relationship: 'target_ref'." in str(excinfo)
+    assert "Missing required field(s) for Relationship: (target_ref)." in str(excinfo)
 
 
 def test_cannot_assign_to_relationship_attributes(relationship):