jinja2cpp
diff --git a/‎src/testers.cpp
Lines changed: 27 additions & 16 deletions b/‎src/testers.cpp
Lines changed: 27 additions & 16 deletions
diff --git a/‎test/testers_test.cpp
Lines changed: 8 additions & 6 deletions b/‎test/testers_test.cpp
Lines changed: 8 additions & 6 deletions
@@ -254,22 +254,33 @@ bool ValueTester::Test(const InternalValue& baseVal, RenderContext& context)
     {
         bool isConverted = false;
         auto seq = GetArgumentValue("seq", context);
-        ListAdapter values = ConvertToList(seq, InternalValue(), isConverted);
-
-        if (!isConverted)
-            return false;
-
-        auto equalComparator = [&baseVal](auto& val) {
-            InternalValue cmpRes;
-
-            cmpRes = Apply2<visitors::BinaryMathOperation>(val, baseVal, BinaryExpression::LogicalEq);
-
-            return ConvertToBool(cmpRes);
-        };
-
-        auto p = std::find_if(values.begin(), values.end(), equalComparator);
-        result = p != values.end();
-
+        auto seqKind = Apply<ValueKindGetter>(seq); 
+        if (seqKind == ValueKind::List) {
+            ListAdapter values = ConvertToList(seq, InternalValue(), isConverted);
+
+            if (!isConverted)
+                return false;
+
+            auto equalComparator = [&baseVal](auto& val) {
+                InternalValue cmpRes;
+                cmpRes = Apply2<visitors::BinaryMathOperation>(val, baseVal, BinaryExpression::LogicalEq);
+                return ConvertToBool(cmpRes);
+            };
+
+            auto p = std::find_if(values.begin(), values.end(), equalComparator);
+            result = p != values.end();
+        } else if (seqKind == ValueKind::String) {
+            result = ApplyStringConverter(baseVal, [&](const auto& srcStr) {
+                    std::decay_t<decltype(srcStr)> emptyStrView;
+                    using CharT = typename decltype(emptyStrView)::value_type;
+                    std::basic_string<CharT> emptyStr;
+
+                    auto substring = sv_to_string(srcStr);
+                    auto seq = GetAsSameString(srcStr, this->GetArgumentValue("seq", context)).value_or(emptyStr);
+
+                    return seq.find(substring) != std::string::npos;
+                });
+        }
         break;
     }
     case IsEvenMode:
 
@@ -242,12 +242,14 @@ INSTANTIATE_TEST_SUITE_P(StringTest, TestersGenericTest, ::testing::Values(
 
 
 INSTANTIATE_TEST_SUITE_P(InTest, TestersGenericTest, ::testing::Values(
-                            InputOutputPair{"0 in (2, 1, 0)",           "true"},
-                            InputOutputPair{"0 in (1, 2, 3)",           "false"},
-                            InputOutputPair{"0 in intList",             "true"},
-                            InputOutputPair{"1000 in intList",          "false"},
-                            InputOutputPair{"'string9' in stringList",  "true"},
-                            InputOutputPair{"'string90' in stringList", "false"}
+                            InputOutputPair{"0 in (2, 1, 0)",             "true"},
+                            InputOutputPair{"0 in (1, 2, 3)",             "false"},
+                            InputOutputPair{"0 in intList",               "true"},
+                            InputOutputPair{"1000 in intList",            "false"},
+                            InputOutputPair{"'string9' in stringList",    "true"},
+                            InputOutputPair{"'string90' in stringList",   "false"},
+                            InputOutputPair{"'string' in 'a big string'", "true"},
+                            InputOutputPair{"'a big string' in 'substr'",  "false"}
                             ));
 
 INSTANTIATE_TEST_SUITE_P(EvenTest, TestersGenericTest, ::testing::Values(