C++: Rewrite local flow test to use TestSig

Author: jketema

cpp/ql/test/library-tests/dataflow/source-sink-tests/local-flow.expected

@@ -0,0 +1,2 @@
+failures
+testFailures

cpp/ql/test/library-tests/dataflow/source-sink-tests/local-flow.ql

@@ -4,12 +4,10 @@ import cpp
 import TestUtilities.InlineExpectationsTest
 import semmle.code.cpp.security.FlowSources
 
-class LocalFlowSourceTest extends InlineExpectationsTest {
-  LocalFlowSourceTest() { this = "LocalFlowSourceTest" }
+module LocalFlowSourceTest implements TestSig {
+  string getARelevantTag() { result = "local_source" }
 
-  override string getARelevantTag() { result = "local_source" }
-
-  override predicate hasActualResult(Location location, string element, string tag, string value) {
+  predicate hasActualResult(Location location, string element, string tag, string value) {
     tag = "local_source" and
     exists(LocalFlowSource node, int n |
       n =
@@ -29,4 +27,10 @@ class LocalFlowSourceTest extends InlineExpectationsTest {
       element = node.toString()
     )
   }
+
+  predicate hasOptionalResult(Location location, string element, string tag, string value) {
+    none()
+  }
 }
+
+import MakeTest<LocalFlowSourceTest>