TestHashFunctions: Tests to bind hash functionality

Problem:
- The hash functions have no associated tests, so there is nothing
  binding their behavior.

Solution:
- Bind the hash function behavior by adding tests.
- Use the existing behavior as "correct".

AK/Tests/TestHashFunctions.cpp

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/TestSuite.h>
+
+#include <AK/HashFunctions.h>
+#include <AK/Types.h>
+
+TEST_CASE(int_hash)
+{
+    EXPECT_EQ(int_hash(42), 3564735745u);
+    EXPECT_EQ(int_hash(0), 1177991625u);
+}
+
+TEST_CASE(double_hash)
+{
+    EXPECT_EQ(double_hash(42), 524450u);
+    EXPECT_EQ(double_hash(0), 12384u);
+}
+
+TEST_CASE(pair_int_hash)
+{
+    EXPECT_EQ(pair_int_hash(42, 17), 339337046u);
+    EXPECT_EQ(pair_int_hash(0, 0), 954888656u);
+}
+
+TEST_CASE(u64_hash)
+{
+    EXPECT_EQ(u64_hash(42), 2824066580u);
+    EXPECT_EQ(u64_hash(0), 954888656u);
+}
+
+TEST_CASE(ptr_hash)
+{
+    if constexpr (sizeof(FlatPtr) == 8) {
+        EXPECT_EQ(ptr_hash(FlatPtr(42)), 2824066580u);
+        EXPECT_EQ(ptr_hash(FlatPtr(0)), 954888656u);
+
+        EXPECT_EQ(ptr_hash(reinterpret_cast<const void*>(42)), 2824066580u);
+        EXPECT_EQ(ptr_hash(reinterpret_cast<const void*>(0)), 954888656u);
+    } else {
+        EXPECT_EQ(ptr_hash(FlatPtr(42)), 3564735745u);
+        EXPECT_EQ(ptr_hash(FlatPtr(0)), 1177991625u);
+
+        EXPECT_EQ(ptr_hash(reinterpret_cast<const void*>(42)), 3564735745u);
+        EXPECT_EQ(ptr_hash(reinterpret_cast<const void*>(0)), 1177991625u);
+    }
+}
+
+TEST_MAIN(HashFunctions)