diff --git a/python/ql/test/3/library-tests/taint/strings/Taint.qll b/python/ql/test/3/library-tests/taint/strings/Taint.qll
new file mode 100644
index 00000000000..3368a1c4f70
--- /dev/null
+++ b/python/ql/test/3/library-tests/taint/strings/Taint.qll
@@ -0,0 +1,44 @@
+import python
+import semmle.python.dataflow.TaintTracking
+import semmle.python.security.strings.Untrusted
+import semmle.python.security.Exceptions
+
+class SimpleSource extends TaintSource {
+  SimpleSource() { this.(NameNode).getId() = "TAINTED_STRING" }
+
+  override predicate isSourceOf(TaintKind kind) { kind instanceof ExternalStringKind }
+
+  override string toString() { result = "taint source" }
+}
+
+class ListSource extends TaintSource {
+  ListSource() { this.(NameNode).getId() = "TAINTED_LIST" }
+
+  override predicate isSourceOf(TaintKind kind) { kind instanceof ExternalStringSequenceKind }
+
+  override string toString() { result = "list taint source" }
+}
+
+class DictSource extends TaintSource {
+  DictSource() { this.(NameNode).getId() = "TAINTED_DICT" }
+
+  override predicate isSourceOf(TaintKind kind) { kind instanceof ExternalStringDictKind }
+
+  override string toString() { result = "dict taint source" }
+}
+
+class ExceptionInfoSource extends TaintSource {
+  ExceptionInfoSource() { this.(NameNode).getId() = "TAINTED_EXCEPTION_INFO" }
+
+  override predicate isSourceOf(TaintKind kind) { kind instanceof ExceptionInfo }
+
+  override string toString() { result = "Exception info source" }
+}
+
+class ExternalFileObjectSource extends TaintSource {
+  ExternalFileObjectSource() { this.(NameNode).getId() = "TAINTED_FILE" }
+
+  override predicate isSourceOf(TaintKind kind) { kind instanceof ExternalFileObject }
+
+  override string toString() { result = "Tainted file source" }
+}
diff --git a/python/ql/test/3/library-tests/taint/strings/TestTaint.expected b/python/ql/test/3/library-tests/taint/strings/TestTaint.expected
new file mode 100644
index 00000000000..6135fb2a756
--- /dev/null
+++ b/python/ql/test/3/library-tests/taint/strings/TestTaint.expected
@@ -0,0 +1 @@
+| test.py:4 | fail | fstring | Fstring | <NO TAINT> |
diff --git a/python/ql/test/3/library-tests/taint/strings/TestTaint.ql b/python/ql/test/3/library-tests/taint/strings/TestTaint.ql
new file mode 100644
index 00000000000..7b9c6025c9d
--- /dev/null
+++ b/python/ql/test/3/library-tests/taint/strings/TestTaint.ql
@@ -0,0 +1,33 @@
+import python
+import semmle.python.security.TaintTracking
+import semmle.python.web.HttpRequest
+import semmle.python.security.strings.Untrusted
+import Taint
+
+from
+  Call call, Expr arg, boolean expected_taint, boolean has_taint, string test_res,
+  string taint_string
+where
+  call.getLocation().getFile().getShortName() = "test.py" and
+  (
+    call.getFunc().(Name).getId() = "ensure_tainted" and
+    expected_taint = true
+    or
+    call.getFunc().(Name).getId() = "ensure_not_tainted" and
+    expected_taint = false
+  ) and
+  arg = call.getAnArg() and
+  (
+    not exists(TaintedNode tainted | tainted.getAstNode() = arg) and
+    taint_string = "<NO TAINT>" and
+    has_taint = false
+    or
+    exists(TaintedNode tainted | tainted.getAstNode() = arg |
+      taint_string = tainted.getTaintKind().toString()
+    ) and
+    has_taint = true
+  ) and
+  if expected_taint = has_taint then test_res = "ok  " else test_res = "fail"
+// if expected_taint = has_taint then test_res = "✓" else test_res = "✕"
+select arg.getLocation().toString(), test_res, call.getScope().(Function).getName(), arg.toString(),
+  taint_string
diff --git a/python/ql/test/3/library-tests/taint/strings/test.py b/python/ql/test/3/library-tests/taint/strings/test.py
new file mode 100644
index 00000000000..e1c25b5dccc
--- /dev/null
+++ b/python/ql/test/3/library-tests/taint/strings/test.py
@@ -0,0 +1,5 @@
+def fstring():
+    tainted_string = TAINTED_STRING
+    ensure_tainted(
+        f"foo {tainted_string} bar"
+    )