add getPrefixList tests

tests/string-set-tests.mlb

@@ -0,0 +1,4 @@
+$(SML_LIB)/basis/basis.mlb
+
+../src/string-set.sml
+string-set-tests.sml

tests/string-set-tests.sml

@@ -0,0 +1,62 @@
+structure StringSetTests =
+struct
+  fun assertTrue (isTrue, msg) =
+    if isTrue then ()
+    else
+      (print (msg ^ "\n"); raise Empty)
+
+  fun assertFalse (isFalse, msg) = assertTrue (not isFalse, msg)
+
+  (* below tests ported from https://github.com/kpol/trie/blob/master/src/KTrie.Tests/TrieTests.cs *)
+
+  fun testExists () =
+    let 
+      val trie = StringSet.fromList ["abc", "abde"]
+
+      val _ = assertTrue (StringSet.exists ("abc", trie), "abc should exist")
+      val _ = assertTrue (StringSet.exists ("abde", trie), "abde should exist")
+
+      val _ = assertFalse (StringSet.exists ("a", trie), "a should not exist")
+      val _ = assertFalse (StringSet.exists ("ab", trie), "ab should not exist")
+      val _ = assertFalse (StringSet.exists ("abcd", trie), "abcd should not exist")
+      val _ = assertFalse (StringSet.exists ("abce", trie), "abce should not exist")
+      val _ = assertFalse (StringSet.exists ("x", trie), "x should not exist")
+    in
+      print "StringSet.exists passed all tests\n"
+    end
+
+  fun testGetPrefixList () =
+    let
+      val trie = StringSet.fromList ["abc", "abde", "abx", "abxx"]
+
+      val aMatches = StringSet.getPrefixList ("a", trie) = ["abc", "abde", "abx", "abxx"]
+      val _ = assertTrue (aMatches, "a matches")
+
+      val xMatches = StringSet.getPrefixList ("x", trie) = []
+      val _ = assertTrue (xMatches, "x matches")
+
+      val abMatches = StringSet.getPrefixList ("ab", trie) = ["abc", "abde", "abx", "abxx"]
+      val _ = assertTrue (abMatches, "ab matches")
+
+      val abcMatches = StringSet.getPrefixList ("abc", trie) = ["abc"]
+      val _ = assertTrue (abcMatches, "abc matches")
+
+      val abccMatches = StringSet.getPrefixList ("abcc", trie) = []
+      val _ = assertTrue (abccMatches, "abcc matches")
+
+      val abxMatches = StringSet.getPrefixList ("abx", trie) = ["abx", "abxx"]
+      val _ = assertTrue (abxMatches, "abx matches")
+    in
+      print "StringSet.getPrefixList passed all tests\n"
+    end
+
+  fun run () =
+    let
+      val _ = testExists ()
+      val _ = testGetPrefixList ()
+    in
+      ()
+    end
+end
+
+val _ = StringSetTests.run ()