Add format width and precision tests.

core/src/fxcrt/fx_basic_wstring_unittest.cpp

Index: core/src/fxcrt/fx_basic_wstring_unittest.cpp
diff --git a/core/src/fxcrt/fx_basic_wstring_unittest.cpp b/core/src/fxcrt/fx_basic_wstring_unittest.cpp
index b75a6fbd39c9f4a870e849aad9e125924dc51681..d49d244a439ba9a812f894b5e790bdb976b3e65d 100644
--- a/core/src/fxcrt/fx_basic_wstring_unittest.cpp
+++ b/core/src/fxcrt/fx_basic_wstring_unittest.cpp
@@ -440,3 +440,31 @@ TEST(fxcrt, WideStringCOperatorNE) {
   EXPECT_TRUE(c_string2 != wide_string_c);
   EXPECT_TRUE(c_string3 != wide_string_c);
 }
+
+TEST(fxcrt, WideStringFormatWidth) {
+  {
+    CFX_WideString str;
+    str.Format(L"%5d", 1);
+    EXPECT_EQ(L"    1", str);
+  }
+
+  {
+    CFX_WideString str;
+    str.Format(L"%d", 1);
+    EXPECT_EQ(L"1", str);
+  }
+}
+
+TEST(fxcrt, WideStringFormatPrecision) {
+  {
+    CFX_WideString str;
+    str.Format(L"%.2f", 1.12345);
+    EXPECT_EQ(L"1.12", str);
+  }
+
+  {
+    CFX_WideString str;
+    str.Format(L"%f", 1.12345);
+    EXPECT_EQ(L"1.123450", str);
+  }
+}