Fix deprecated 3.6 backslash-character pairs

(https://docs.python.org/3/whatsnew/3.6.html#deprecated-python-behavior)

stix2/test/test_external_reference.py

@@ -42,7 +42,7 @@ def test_external_reference_capec():
     )
 
     assert str(ref) == CAPEC
-    assert re.match("ExternalReference\(source_name=u?'capec', external_id=u?'CAPEC-550'\)", repr(ref))
+    assert re.match("ExternalReference\\(source_name=u?'capec', external_id=u?'CAPEC-550'\\)", repr(ref))
 
 
 CAPEC_URL = """{
@@ -109,7 +109,7 @@ def test_external_reference_offline():
     )
 
     assert str(ref) == OFFLINE
-    assert re.match("ExternalReference\(source_name=u?'ACME Threat Intel', description=u?'Threat report'\)", repr(ref))
+    assert re.match("ExternalReference\\(source_name=u?'ACME Threat Intel', description=u?'Threat report'\\)", repr(ref))
     # Yikes! This works
     assert eval("stix2." + repr(ref)) == ref
 

stix2/test/test_malware.py

@@ -126,7 +126,7 @@ def test_parse_malware(data):
 
 
 def test_parse_malware_invalid_labels():
-    data = re.compile('\[.+\]', re.DOTALL).sub('1', EXPECTED_MALWARE)
+    data = re.compile('\\[.+\\]', re.DOTALL).sub('1', EXPECTED_MALWARE)
     with pytest.raises(ValueError) as excinfo:
         stix2.parse(data)
     assert "Invalid value for Malware 'labels'" in str(excinfo.value)

stix2/test/test_pattern_expressions.py

@@ -319,13 +319,13 @@ def test_invalid_binary_constant():
 
 def test_escape_quotes_and_backslashes():
     exp = stix2.MatchesComparisonExpression("file:name",
-                                            "^Final Report.+\.exe$")
+                                            "^Final Report.+\\.exe$")
     assert str(exp) == "file:name MATCHES '^Final Report.+\\\\.exe$'"
 
 
 def test_like():
     exp = stix2.LikeComparisonExpression("directory:path",
-                                         "C:\Windows\%\\foo")
+                                         "C:\\Windows\\%\\foo")
     assert str(exp) == "directory:path LIKE 'C:\\\\Windows\\\\%\\\\foo'"