Index: uspace/lib/cpp/src/internal/test/string.cpp
===================================================================
--- uspace/lib/cpp/src/internal/test/string.cpp	(revision d3bca357377316e73ef7bf2d7b5920c1a97b2db2)
+++ uspace/lib/cpp/src/internal/test/string.cpp	(revision 6c089a909193b6401c87f8f44b601583ce81b926)
@@ -410,5 +410,5 @@
         idx = str1.rfind(target, miss);
         test_eq(
-            "rfind from start (success)",
+            "rfind from end (success)",
             idx, 2ul
         );
@@ -418,4 +418,16 @@
             "rfind from start (fail, late start)",
             idx, miss
+        );
+
+        idx = str1.find('B', 2);
+        test_eq(
+            "find char from middle (success)",
+            idx, 3ul
+        );
+
+        idx = str1.rfind('B', 2);
+        test_eq(
+            "rfind char from middle (success)",
+            idx, 3ul
         );
 
@@ -427,4 +439,196 @@
             idx, 2ul
         );
+
+        idx = str2.find(target, 5);
+        test_eq(
+            "find from middle (success, multiple)",
+            idx, 7ul
+        );
+
+        idx = str2.rfind(target, miss);
+        test_eq(
+            "rfind from end (success, multiple)",
+            idx, 7ul
+        );
+
+        idx = str2.rfind(target, 6);
+        test_eq(
+            "rfind from mid (success, multiple)",
+            idx, 2ul
+        );
+
+        std::string str3{"xxBxxAxxCxx"};
+
+        idx = str3.find_first_of(target);
+        test_eq(
+            "find first of from start (success)",
+            idx, 2ul
+        );
+
+        idx = str3.find_first_of(target, 6);
+        test_eq(
+            "find first of from middle (success)",
+            idx, 8ul
+        );
+
+        idx = str3.find_first_of("DEF", 3);
+        test_eq(
+            "find first of from middle (fail, not in string)",
+            idx, miss
+        );
+
+        idx = str3.find_first_of(target, 9);
+        test_eq(
+            "find first of from middle (fail, late start)",
+            idx, miss
+        );
+
+        idx = str3.find_first_of("");
+        test_eq(
+            "find first of from start (fail, no target)",
+            idx, miss
+        );
+
+        idx = str3.find_first_of('A', 1);
+        test_eq(
+            "find first of char (success)",
+            idx, 5ul
+        );
+
+        idx = str3.find_first_of('A', 6);
+        test_eq(
+            "find first of char (fail)",
+            idx, miss
+        );
+
+        idx = str3.find_last_of(target);
+        test_eq(
+            "find last of from start (success)",
+            idx, 8ul
+        );
+
+        idx = str3.find_last_of(target, 6);
+        test_eq(
+            "find last of from middle (success)",
+            idx, 5ul
+        );
+
+        idx = str3.find_last_of("DEF", 3);
+        test_eq(
+            "find last of from middle (fail, not in string)",
+            idx, miss
+        );
+
+        idx = str3.find_last_of(target, 1);
+        test_eq(
+            "find last of from middle (fail, late start)",
+            idx, miss
+        );
+
+        idx = str3.find_last_of("");
+        test_eq(
+            "find last of from start (fail, no target)",
+            idx, miss
+        );
+
+        idx = str3.find_last_of('A', str3.size() - 1);
+        test_eq(
+            "find last of char (success)",
+            idx, 5ul
+        );
+
+        idx = str3.find_last_of('A', 3);
+        test_eq(
+            "find last of char (fail)",
+            idx, miss
+        );
+
+        std::string not_target{"xB"};
+
+        idx = str3.find_first_not_of(not_target);
+        test_eq(
+            "find first not of from start (success)",
+            idx, 5ul
+        );
+
+        idx = str3.find_first_not_of(not_target, 6);
+        test_eq(
+            "find first not of from middle (success)",
+            idx, 8ul
+        );
+
+        idx = str3.find_first_not_of("xABC", 3);
+        test_eq(
+            "find first not of from middle (fail, not in string)",
+            idx, miss
+        );
+
+        idx = str3.find_first_not_of(not_target, 9);
+        test_eq(
+            "find first not of from middle (fail, late start)",
+            idx, miss
+        );
+
+        idx = str3.find_first_not_of("");
+        test_eq(
+            "find first not of from start (success, no target)",
+            idx, 0ul
+        );
+
+        idx = str3.find_first_not_of('x', 3);
+        test_eq(
+            "find first not of char (success)",
+            idx, 5ul
+        );
+
+        idx = str3.find_first_of('a', 9);
+        test_eq(
+            "find first not of char (fail)",
+            idx, miss
+        );
+
+        std::string not_last_target{"xC"};
+
+        idx = str3.find_last_not_of(not_last_target);
+        test_eq(
+            "find last not of from start (success)",
+            idx, 5ul
+        );
+
+        idx = str3.find_last_not_of(not_last_target, 4);
+        test_eq(
+            "find last not of from middle (success)",
+            idx, 2ul
+        );
+
+        idx = str3.find_last_not_of("xABC");
+        test_eq(
+            "find last not of from middle (fail, not in string)",
+            idx, miss
+        );
+
+        idx = str3.find_last_not_of(not_last_target, 1);
+        test_eq(
+            "find last not of from middle (fail, late start)",
+            idx, miss
+        );
+
+        idx = str3.find_last_not_of("");
+        test_eq(
+            "find last not of from start (success, no target)",
+            idx, str3.size() - 1
+        );
+
+        idx = str3.find_last_not_of('x', str3.size() - 1);
+        test_eq(
+            "find last not of char (success)",
+            idx, 8ul
+        );
+
+        idx = str3.find_last_not_of('x', 1);
+        test_eq(
+            "find last not of char (fail)",
+            idx, miss
+        );
     }
 }