Add some tests for the union type

analyzer/type_test.go

@@ -148,6 +148,29 @@ Bird: (.
 `)
 }
 
+func TestTypeUnion (test *testing.T) {
+testString (test,
+`
+U: (| I8 I16 I32 I64 Int)
+Point: (. x:Int y:Int)
+Error: (~ [error]:String)
+PointOrError: (| Point Error)
+`)
+}
+
+func TestTypeUnionAllowedUniqueErr (test *testing.T) {
+testStringErr (test,
+"(. x:Int) already listed in union at stream0.fspl:5:3", 7, 3,
+`
+U: (|
+	U8
+	U16
+	(. x:Int)
+	Int
+	(. x:Int))
+`)
+}
+
 func TestTypeInterfaceBehaviorUniqueErr (test *testing.T) {
 testStringErr (test,
 "fly already listed in interface at stream0.fspl:2:10", 2, 16,