PS: Add failing tests.

Author: MathiasVP

powershell/ql/test/library-tests/dataflow/returns/test.expected

@@ -0,0 +1,6 @@
+models
+edges
+nodes
+subpaths
+testFailures
+#select

powershell/ql/test/library-tests/dataflow/returns/test.ps1

@@ -0,0 +1,31 @@
+function callSourceOnce {
+    Source "1"
+}
+
+$x = callSourceOnce
+Sink $x # $ MISSING: hasValueFlow=1
+
+function callSourceTwice {
+    Source "2"
+    Source "3"
+}
+
+$x = callSourceTwice
+Sink $x # $ MISSING: hasValueFlow=2 hasValueFlow=3
+
+function returnSource1 {
+    return Source "4"
+}
+
+$x = returnSource1
+Sink $x # $ MISSING: hasValueFlow=4
+
+function returnSource2 {
+    $x = Source "5"
+    $x
+    $y = Source "6"
+    return $y
+}
+
+$x = returnSource2
+Sink $x # $ MISSING: hasValueFlow=5 hasValueFlow=6

powershell/ql/test/library-tests/dataflow/returns/test.ql

@@ -0,0 +1,13 @@
+/**
+ * @kind path-problem
+ */
+
+import powershell
+import semmle.code.powershell.dataflow.DataFlow
+private import TestUtilities.InlineFlowTest
+import DefaultFlowTest
+import ValueFlow::PathGraph
+
+from ValueFlow::PathNode source, ValueFlow::PathNode sink
+where ValueFlow::flowPath(source, sink)
+select sink, source, sink, "$@", source, source.toString()