diff --git a/poincare/test/helper.cpp b/poincare/test/helper.cpp
index ac173bb4c..9ef5a106a 100644
--- a/poincare/test/helper.cpp
+++ b/poincare/test/helper.cpp
@@ -59,14 +59,23 @@ void translate_in_ASCII_chars(char * expression) {
   }
 }
 
-Expression parse_expression(const char * expression) {
+Expression parse_expression(const char * expression, bool canBeUnparsable) {
+  quiz_print(expression);
   char buffer[500];
   strlcpy(buffer, expression, sizeof(buffer));
   translate_in_special_chars(buffer);
   Expression result = Expression::parse(buffer);
+  if (!canBeUnparsable) {
+    quiz_assert(!result.isUninitialized());
+  }
   return result;
 }
 
+void assert_expression_not_parsable(const char * expression) {
+  Expression e = parse_expression(expression, true);
+  quiz_assert(e.isUninitialized());
+}
+
 void assert_parsed_expression_type(const char * expression, Poincare::ExpressionNode::Type type) {
   Expression e = parse_expression(expression);
   quiz_assert(e.type() == type);
diff --git a/poincare/test/helper.h b/poincare/test/helper.h
index a1a7b782b..e9befed7d 100644
--- a/poincare/test/helper.h
+++ b/poincare/test/helper.h
@@ -17,7 +17,8 @@ constexpr Poincare::Preferences::PrintFloatMode ScientificMode = Poincare::Prefe
 
 void translate_in_special_chars(char * expression);
 void translate_in_ASCII_chars(char * expression);
-Poincare::Expression parse_expression(const char * expression);
+Poincare::Expression parse_expression(const char * expression, bool canBeUnparsable = false);
+void assert_expression_not_parsable(const char * expression);
 void assert_parsed_expression_type(const char * expression, Poincare::ExpressionNode::Type type);
 void assert_parsed_expression_is(const char * expression, Poincare::Expression r);
 void assert_parsed_expression_polynomial_degree(const char * expression, int degree, const char * symbolName = "x");
diff --git a/poincare/test/store.cpp b/poincare/test/store.cpp
index 08f7b7e5b..f0e858f3c 100644
--- a/poincare/test/store.cpp
+++ b/poincare/test/store.cpp
@@ -58,3 +58,27 @@ QUIZ_CASE(poincare_store_user_variable) {
   Ion::Storage::sharedStorage()->recordNamed("f2.func").destroy();
   Ion::Storage::sharedStorage()->recordNamed("funcBoth.func").destroy();
 }
+
+QUIZ_CASE(poincare_store_that_should_fail) {
+  // Create a helper function
+  assert_parsed_expression_simplify_to("1>g(x)", "1");
+
+  // Store only works on variables or functions
+  assert_expression_not_parsable("2>f(2)");
+  assert_expression_not_parsable("3>f(g(4))");
+
+  // Clean the storage for other tests
+  Ion::Storage::sharedStorage()->recordNamed("g.func").destroy();
+}
+
+QUIZ_CASE(poincare_store_overwrite) {
+  assert_parsed_expression_simplify_to("-1>g(x)", "-1");
+  assert_parsed_expression_simplify_to("1+g(x)>f(x)", "1+g(?)");
+  assert_parsed_expression_simplify_to("2>g", "2");
+  assert_parsed_expression_evaluates_to<double>("g(4)", "undef");
+  assert_parsed_expression_evaluates_to<double>("f(4)", "undef");
+
+  // Clean the storage for other tests
+  Ion::Storage::sharedStorage()->recordNamed("f.func").destroy();
+  Ion::Storage::sharedStorage()->recordNamed("g.exp").destroy();
+}