Expanded test and clean implementation

Author: WillAyd

pandas/_libs/src/ujson/lib/ultrajsonenc.c

@@ -1003,7 +1003,7 @@ void encode(JSOBJ obj, JSONObjectEncoder *enc, const char *name,
 
             Buffer_AppendCharUnchecked(enc, '{');
 	    Buffer_AppendIndentNewlineUnchecked (enc);
-	    Buffer_AppendIndentUnchecked (enc, enc->level + 2);
+	    Buffer_AppendIndentUnchecked (enc, enc->level);
 
             while (enc->iterNext(obj, &tc)) {
                 if (count > 0) {
@@ -1012,7 +1012,7 @@ void encode(JSOBJ obj, JSONObjectEncoder *enc, const char *name,
                     Buffer_AppendCharUnchecked(enc, ' ');
 #endif
 		    Buffer_AppendIndentNewlineUnchecked (enc);
-		    Buffer_AppendIndentUnchecked (enc, enc->level + 2);
+		    Buffer_AppendIndentUnchecked (enc, enc->level);
                 }
 
                 iterObj = enc->iterGetValue(obj, &tc);
@@ -1025,7 +1025,7 @@ void encode(JSOBJ obj, JSONObjectEncoder *enc, const char *name,
 
             enc->iterEnd(obj, &tc);
 	    Buffer_AppendIndentNewlineUnchecked (enc);
-	    Buffer_AppendIndentUnchecked (enc, enc->level + 1);
+	    Buffer_AppendIndentUnchecked (enc, enc->level);
             Buffer_AppendCharUnchecked(enc, '}');
             break;
         }

pandas/tests/io/json/test_pandas.py

@@ -1648,22 +1648,24 @@ def test_tuple_labels(self, orient, expected):
         result = df.to_json(orient=orient)
         assert result == expected
 
-    def test_to_json_indent(self):
+    @pytest.mark.parametrize("indent", [1, 2, 4])
+    def test_to_json_indent(self, indent):
         # GH 12004
         df = pd.DataFrame([
             ['foo', 'bar'], ['baz', 'qux']
         ], columns=['a', 'b'])
 
-        result = df.to_json(indent=4)
-        expected = """{
-    "a":{
-        "0":"foo",
-        "1":"baz"
-    },
-    "b":{
-        "0":"bar",
-        "1":"qux"
-    }
-}"""
+        result = df.to_json(indent=indent)
+        spaces = " " * indent
+        expected = """{{
+"a":{{
+{spaces}"0":"foo",
+{spaces}"1":"baz"
+{spaces}}},
+"b":{{
+{spaces}"0":"bar",
+{spaces}"1":"qux"
+{spaces}}}
+}}""".format(spaces=spaces)
 
         assert result == expected