mac: add SysNSString{To,From}UTF{8,16} test coverage

Bug: 27059
Change-Id: I135c1bbd498cf4d3769718f91ddd486d2cd4c9af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2106564
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751337}

base/strings/sys_string_conversions_mac_unittest.mm

@@ -6,6 +6,7 @@
 
 #include "base/strings/string16.h"
 #include "base/strings/sys_string_conversions.h"
+#include "base/strings/utf_string_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
@@ -18,4 +19,36 @@ TEST(SysStrings, ConversionsFromNSString) {
   EXPECT_EQ(string16(), SysNSStringToUTF16(nil));
 }
 
+std::vector<std::string> GetRoundTripStrings() {
+  return {
+      "Hello, World!",    // ASCII / ISO8859 string (also valid UTF-8)
+      {'a', 0, 'b'},      // UTF-8 with embedded NUL byte
+      {0xce, 0xbb, 'f'},  // lowercase lambda + 'f'
+      "χρώμιο",           // "chromium" in greek
+      "כרום",             // "chromium" in hebrew
+      "クロム",           // "chromium" in japanese
+
+      // Tarot card symbol "the morning", which does not fit in one UTF-16
+      // character.
+      u8"\U0001f0e6",
+  };
+}
+
+TEST(SysStrings, RoundTripsFromUTF8) {
+  for (const auto& string8 : GetRoundTripStrings()) {
+    NSString* nsstring8 = SysUTF8ToNSString(string8);
+    std::string back8 = SysNSStringToUTF8(nsstring8);
+    EXPECT_EQ(string8, back8);
+  }
+}
+
+TEST(SysStrings, RoundTripsFromUTF16) {
+  for (const auto& string8 : GetRoundTripStrings()) {
+    base::string16 string16 = base::UTF8ToUTF16(string8);
+    NSString* nsstring16 = SysUTF16ToNSString(string16);
+    base::string16 back16 = SysNSStringToUTF16(nsstring16);
+    EXPECT_EQ(string16, back16);
+  }
+}
+
 }  // namespace base