tests/Hints: add test for recently added hint

Added in d703c55 .

Author: knocte

tests/FSharpLint.Core.Tests/Rules/Hints/HintMatcher.fs

@@ -953,4 +953,15 @@ let x y =
 
         this.SetConfig(["List.map f (List.map g x) ===> List.map (g >> f) x"])
         this.Parse(source)
-        Assert.AreEqual(expected, this.ApplyQuickFix source)
+        Assert.AreEqual(expected, this.ApplyQuickFix source)
+
+    [<Test>]
+    member this.``List append of singleton item can be replaced with :: operator``() =
+        let source = """[head] @ tail"""
+
+        let expected = """head :: tail"""
+
+        this.SetConfig(["[x] @ y ===> x::y"])
+        this.Parse(source)
+        Assert.AreEqual(expected, this.ApplyQuickFix source)
+