test: Add span unit tests

test/unittests/CMakeLists.txt

@@ -19,6 +19,7 @@ target_sources(
     leb128_test.cpp
     parser_expr_test.cpp
     parser_test.cpp
+    span_test.cpp
     stack_test.cpp
     test_utils_test.cpp
     types_test.cpp

test/unittests/span_test.cpp

@@ -0,0 +1,64 @@
+// Fizzy: A fast WebAssembly interpreter
+// Copyright 2020 The Fizzy Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+#include "span.hpp"
+#include "stack.hpp"
+#include <gtest/gtest.h>
+
+using namespace fizzy;
+using namespace testing;
+
+TEST(span, vector)
+{
+    std::vector<uint64_t> vec{1, 2, 3, 4, 5, 6};
+    span<const uint64_t> s(&vec[1], 3);
+    EXPECT_EQ(s.size(), 3);
+    EXPECT_EQ(s[0], 2);
+    EXPECT_EQ(s[1], 3);
+    EXPECT_EQ(s[2], 4);
+    EXPECT_EQ(*s.begin(), 2);
+    EXPECT_EQ(*(s.end() - 1), 4);
+
+    vec[1] = 100;
+    EXPECT_EQ(s[0], 100);
+
+    const auto s2 = span<const uint64_t>(vec);
+    for (size_t i = 0; i < vec.size(); ++i)
+        EXPECT_EQ(s2[i], vec[i]);
+}
+
+TEST(span, stack)
+{
+    OperandStack stack(4);
+    stack.push(10);
+    stack.push(11);
+    stack.push(12);
+    stack.push(13);
+
+    constexpr auto num_items = 2;
+    span<const uint64_t> s(stack.rend() - num_items, num_items);
+    EXPECT_EQ(s.size(), 2);
+    EXPECT_EQ(s[0], 12);
+    EXPECT_EQ(s[1], 13);
+
+    stack[0] = 0;
+    EXPECT_EQ(s[1], 0);
+}
+
+TEST(span, initializer_list)
+{
+    // Dangerous usage because user need to keep the initializer_list alive
+    // as long as span is being used.
+    const std::initializer_list<uint64_t> init = {1, 2, 3};
+    const auto s = span<const uint64_t>(init);
+    EXPECT_EQ(s.size(), 3);
+    EXPECT_EQ(s[0], 1);
+    EXPECT_EQ(s[1], 2);
+    EXPECT_EQ(s[2], 3);
+
+    // For range loop also works.
+    uint64_t i = 0;
+    for (const auto& x : s)
+        EXPECT_EQ(x, ++i);
+}