diff --git a/src/querytyper/mongo/query.py b/src/querytyper/mongo/query.py
index 1084ada..70a6130 100644
--- a/src/querytyper/mongo/query.py
+++ b/src/querytyper/mongo/query.py
@@ -55,11 +55,29 @@ def __or__(
 
 
 class QueryCondition(DictStrAny):
-    """MongoQuery condition."""
+    """Class to represent a single query condition."""
 
     def __init__(self, *args: Any, **kwargs: DictStrAny) -> None:
-        """Overload init typing."""
-        super().__init__(*args, **kwargs)
+        """
+        Initialize a QueryCondition instance.
+
+        It should receive a dict as only argument.
+
+        Example
+        -------
+        ```python
+        QueryCondition({"field": "value"})
+        ```
+
+        It also overloads dict __init__ typing.
+        """
+        arg = args[0]
+        if len(args) != 1 or not isinstance(arg, dict):
+            raise TypeError("QueryCondition must receive only one dict as input.")
+        if isinstance(arg, dict):
+            super().__init__(**arg)
+            for k, v in arg.items():
+                self.__setitem__(k, v)
 
     def __and__(
         self,
@@ -149,6 +167,13 @@ def __le__(
         """Overload <= operator."""
         return self == {"$lte": other}
 
+    def __contains__(
+        self,
+        other: T,
+    ) -> QueryCondition:
+        """Overload in operator."""
+        return regex_query(self.name, re.compile(other))
+
 
 def exists(
     field: Any,
@@ -165,6 +190,8 @@ def regex_query(
     field: Union[QueryField[str], str],
     regex: re.Pattern,
 ) -> QueryCondition:
-    if isinstance(field, QueryField):
-        return QueryCondition({field.name: {"$regex": regex.pattern}})
-    return QueryCondition({field: {"$regex": regex.pattern}})
+    return (
+        QueryCondition({field.name: {"$regex": regex.pattern}})
+        if isinstance(field, QueryField)
+        else QueryCondition({field: {"$regex": regex.pattern}})
+    )
diff --git a/tests/mongo/conftest.py b/tests/mongo/conftest.py
index 7d3846b..15190ec 100644
--- a/tests/mongo/conftest.py
+++ b/tests/mongo/conftest.py
@@ -1,5 +1,6 @@
 """Tests fixtures and configurations."""
 from typing import Dict, List, Optional
+
 from pydantic import BaseModel
 
 from querytyper import MongoFilterMeta
diff --git a/tests/mongo/test_pymongo_integration.py b/tests/mongo/test_pymongo_integration.py
index 51ce123..01ae691 100644
--- a/tests/mongo/test_pymongo_integration.py
+++ b/tests/mongo/test_pymongo_integration.py
@@ -1,9 +1,10 @@
 """Test querytyper integration with pymongo."""
-import re
 from typing import Any, Dict
+
 from mongomock import MongoClient
 
-from querytyper import MongoQuery, regex_query
+from querytyper import MongoQuery
+
 from .conftest import Dummy, QueryModel
 
 
@@ -23,10 +24,12 @@ def test_integration_with_pymongo() -> None:
             for i in range(doc_num)
         ]
     )
-    # found_doc = collection.find_one(MongoQuery(QueryModel.int_field == 1)._query_dict)
     found_doc = collection.find_one(MongoQuery(QueryModel.int_field == 1))
     assert found_doc is not None
     found_dummy = Dummy(**found_doc)
     assert found_dummy.int_field == 1
-    found_docs = list(collection.find(MongoQuery(regex_query(QueryModel.str_field, re.compile("test")))))
-    assert len(found_docs) == doc_num
\ No newline at end of file
+    query = MongoQuery("test" in QueryModel.str_field)
+    assert isinstance(query, dict)
+    # assert query
+    found_docs = list(collection.find(query))
+    assert len(found_docs) == doc_num
diff --git a/tests/mongo/test_query.py b/tests/mongo/test_query.py
index 07ba4c1..eb02121 100644
--- a/tests/mongo/test_query.py
+++ b/tests/mongo/test_query.py
@@ -179,3 +179,13 @@ def test_exists_query() -> None:
         TypeError, match="Field must be a QueryField or str, <class 'int'> is not supported."
     ):
         exists(1)
+
+
+def test_query_condition_init() -> None:
+    """Test QueryCondition initializer and TypeErrors."""
+    with pytest.raises(TypeError, match="QueryCondition must receive only one dict as input."):
+        QueryCondition(1)
+        QueryCondition(1, 2, 3)
+    condition = QueryCondition({"field": "value"})
+    assert "field" in condition
+    assert condition["field"] == "value"