Remove mutable from some tests

Author: mahdihasnat

Algorithms.Tests/DataStructures/Trie.fs

@@ -30,19 +30,20 @@ type TrieTests () =
 
     [<TestMethod>]
     member this.``Test insert empty key``() =
-        let mutable trie = empty
+        let trie =
+            empty
+            |> insert ""
 
-        trie <- insert "" trie
         Assert.IsTrue(search "" trie)
         Assert.IsFalse(search "foo" trie)
 
     [<TestMethod>]
     member this.``Test overlapping keys``() =
-        let mutable trie = empty
-
-        trie <- insert "car" trie
-        trie <- insert "cart" trie
-        trie <- insert "carter" trie
+        let trie =
+            empty
+            |> insert "car"
+            |> insert "cart"
+            |> insert "carter"
 
         Assert.IsTrue(search "car" trie)
         Assert.IsTrue(search "cart" trie)
@@ -51,9 +52,10 @@ type TrieTests () =
 
     [<TestMethod>]
     member this.``Test partial match``() =
-        let mutable trie = empty
+        let trie =
+            empty
+            |> insert "apple"
 
-        trie <- insert "apple" trie
         Assert.IsFalse(search "app" trie)
         Assert.IsFalse(search "appl" trie)
         Assert.IsTrue(search "apple" trie)