tests/extmod: Improve ujson coverage.

tests/extmod/ujson_loads.py

@@ -23,6 +23,12 @@ my_print(json.loads('{}'))
 my_print(json.loads('{"a":true}'))
 my_print(json.loads('{"a":null, "b":false, "c":true}'))
 my_print(json.loads('{"a":[], "b":[1], "c":{"3":4}}'))
+my_print(json.loads('"abc\\bdef"'))
+my_print(json.loads('"abc\\fdef"'))
+my_print(json.loads('"abc\\ndef"'))
+my_print(json.loads('"abc\\rdef"'))
+my_print(json.loads('"abc\\tdef"'))
+my_print(json.loads('"abc\\uabcd"'))
 
 # whitespace handling
 my_print(json.loads('{\n\t"a":[]\r\n, "b":[1], "c":{"3":4}     \n\r\t\r\r\r\n}'))
@@ -32,3 +38,33 @@ try:
     json.loads('')
 except ValueError:
     print('ValueError')
+
+# string which is not closed
+try:
+    my_print(json.loads('"abc'))
+except ValueError:
+    print('ValueError')
+
+# unaccompanied closing brace
+try:
+    my_print(json.loads(']'))
+except ValueError:
+    print('ValueError')
+
+# unspecified object type
+try:
+    my_print(json.loads('a'))
+except ValueError:
+    print('ValueError')
+
+# bad property name
+try:
+    my_print(json.loads('{{}:"abc"}'))
+except ValueError:
+    print('ValueError')
+
+# unexpected characters after white space
+try:
+    my_print(json.loads('[null]   a'))
+except ValueError:
+    print('ValueError')