diff --git a/test/unittest/prettywritertest.cpp b/test/unittest/prettywritertest.cpp
index b18ad3f..6ae14b9 100644
--- a/test/unittest/prettywritertest.cpp
+++ b/test/unittest/prettywritertest.cpp
@@ -22,10 +22,28 @@
 #include "rapidjson/reader.h"
 #include "rapidjson/prettywriter.h"
 #include "rapidjson/stringbuffer.h"
+#include "rapidjson/filewritestream.h"
 
 using namespace rapidjson;
 
 static const char kJson[] = "{\"hello\":\"world\",\"t\":true,\"f\":false,\"n\":null,\"i\":123,\"pi\":3.1416,\"a\":[1,2,3,-1],\"u64\":1234567890123456789,\"i64\":-1234567890123456789}";
+static const char kPrettyJson[] =
+"{\n"
+"    \"hello\": \"world\",\n"
+"    \"t\": true,\n"
+"    \"f\": false,\n"
+"    \"n\": null,\n"
+"    \"i\": 123,\n"
+"    \"pi\": 3.1416,\n"
+"    \"a\": [\n"
+"        1,\n"
+"        2,\n"
+"        3,\n"
+"        -1\n"
+"    ],\n"
+"    \"u64\": 1234567890123456789,\n"
+"    \"i64\": -1234567890123456789\n"
+"}";
 
 TEST(PrettyWriter, Basic) {
     StringBuffer buffer;
@@ -33,24 +51,7 @@ TEST(PrettyWriter, Basic) {
     Reader reader;
     StringStream s(kJson);
     reader.Parse(s, writer);
-    EXPECT_STREQ(
-        "{\n"
-        "    \"hello\": \"world\",\n"
-        "    \"t\": true,\n"
-        "    \"f\": false,\n"
-        "    \"n\": null,\n"
-        "    \"i\": 123,\n"
-        "    \"pi\": 3.1416,\n"
-        "    \"a\": [\n"
-        "        1,\n"
-        "        2,\n"
-        "        3,\n"
-        "        -1\n"
-        "    ],\n"
-        "    \"u64\": 1234567890123456789,\n"
-        "    \"i64\": -1234567890123456789\n"
-        "}",
-        buffer.GetString());
+    EXPECT_STREQ(kPrettyJson, buffer.GetString());
 }
 
 TEST(PrettyWriter, SetIndent) {
@@ -137,22 +138,30 @@ TEST(PrettyWriter, OStreamWrapper) {
     reader.Parse(s, writer);
     
     std::string actual = ss.str();
-    EXPECT_STREQ(
-        "{\n"
-        "    \"hello\": \"world\",\n"
-        "    \"t\": true,\n"
-        "    \"f\": false,\n"
-        "    \"n\": null,\n"
-        "    \"i\": 123,\n"
-        "    \"pi\": 3.1416,\n"
-        "    \"a\": [\n"
-        "        1,\n"
-        "        2,\n"
-        "        3,\n"
-        "        -1\n"
-        "    ],\n"
-        "    \"u64\": 1234567890123456789,\n"
-        "    \"i64\": -1234567890123456789\n"
-        "}",
-        actual.c_str());
+    EXPECT_STREQ(kPrettyJson, actual.c_str());
 }
+
+// For covering FileWriteStream::PutN()
+TEST(PrettyWriter, FileWriteStream) {
+    char filename[L_tmpnam];
+    FILE* fp = TempFile(filename);
+    char buffer[16];
+    FileWriteStream os(fp, buffer, sizeof(buffer));
+    PrettyWriter<FileWriteStream> writer(os);
+    Reader reader;
+    StringStream s(kJson);
+    reader.Parse(s, writer);
+    fclose(fp);
+
+    fp = fopen(filename, "rb");
+    fseek(fp, 0, SEEK_END);
+    size_t size = (size_t)ftell(fp);
+    fseek(fp, 0, SEEK_SET);
+    char* json = (char*)malloc(size + 1);
+    size_t readLength = fread(json, 1, size, fp);
+    json[readLength] = '\0';
+    fclose(fp);
+    remove(filename);
+    EXPECT_STREQ(kPrettyJson, json);
+    free(json);
+}
\ No newline at end of file