Add failing test for 'ToString() returns null bug'

Author: rojepp

tests/fsharpqa/Source/InteractiveSession/Misc/ToStringNull.fsx

@@ -0,0 +1,12 @@
+// #Regression #NoMT #FSI 
+// Microsoft.Analysis.Server overrides ToString() to return isNull
+// instead of a string. This would make FSI fail in pretty-printing 
+// when displaying results. 
+//<Expects status="success">val n : NullToString = </Expects>
+
+type NullToString() = 
+  override __.ToString() = null;;
+
+let n = NullToString();;
+#q;;
+

tests/fsharpqa/Source/InteractiveSession/Misc/env.lst

@@ -27,6 +27,8 @@ ReqENU	SOURCE=E_InterfaceCrossConstrained02.fsx   COMPILE_ONLY=1 FSIMODE=PIPE SC
 
 	SOURCE=EmptyList.fsx COMPILE_ONLY=1 FSIMODE=PIPE SCFLAGS="--nologo"	# EmptyList.fsx
 
+	SOURCE=ToStringNull.fsx COMPILE_ONLY=1 FSIMODE=PIPE SCFLAGS="--nologo"	# ToStringNull.fsx
+
 # These are the regression tests for FSHARP1.0:5427
 # The scenario is a bit convoluted because of the way we end up doing the verification
 # In the last 2 cases, the verification is achieved by dumping the output of FSI to a file