diff --git a/tests/StringTest.cpp b/tests/StringTest.cpp
index e20732a186..0a7d375a07 100644
--- a/tests/StringTest.cpp
+++ b/tests/StringTest.cpp
@@ -162,33 +162,35 @@ DEF_TEST(String, reporter) {
     }
 
     REPORTER_ASSERT(reporter, SkStringPrintf("%i", 0).equals("0"));
+}
 
+static void assert_2000_spaces(skiatest::Reporter* reporter, const SkString& str) {
+    REPORTER_ASSERT(reporter, str.size() == 2000);
+    for (size_t i = 0; i < str.size(); ++i) {
+        REPORTER_ASSERT(reporter, str[i] == ' ');
+    }
+}
+
+DEF_TEST(String_overflow, reporter) {
     // 2000 is larger than the static buffer size inside SkString.cpp
-    a = SkStringPrintf("%2000s", " ");
-    REPORTER_ASSERT(reporter, a.size() == 2000);
-    for (size_t i = 0; i < a.size(); ++i) {
-        if (a[i] != ' ') {
-            ERRORF(reporter, "SkStringPrintf fail: a[%zu] = '%c'", i, a[i]);
-            break;
-        }
-    }
-    a.reset();
+    SkString a = SkStringPrintf("%2000s", " ");
+    assert_2000_spaces(reporter, a);
+
+    a = "X";
     a.printf("%2000s", " ");
-    REPORTER_ASSERT(reporter, a.size() == 2000);
-    for (size_t i = 0; i < a.size(); ++i) {
-        if (a[i] != ' ') {
-            ERRORF(reporter, "SkString::printf fail: a[%zu] = '%c'", i, a[i]);
-            break;
-        }
-    }
-    a.appendf("%2000s", " ");
-    REPORTER_ASSERT(reporter, a.size() == 4000);
-    for (size_t i = 0; i < a.size(); ++i) {
-        if (a[i] != ' ') {
-            ERRORF(reporter, "SkString::appendf fail: a[%zu] = '%c'", i, a[i]);
-            break;
-        }
-    }
+    assert_2000_spaces(reporter, a);
+
+    a = "X";
+    a.appendf("%1999s", " ");
+    REPORTER_ASSERT(reporter, a[0] == 'X');
+    a[0] = ' ';
+    assert_2000_spaces(reporter, a);
+
+    a = "X";
+    a.prependf("%1999s", " ");
+    REPORTER_ASSERT(reporter, a[1999] == 'X');
+    a[1999] = ' ';
+    assert_2000_spaces(reporter, a);
 }
 
 DEF_TEST(String_SkStrSplit, r) {
@@ -320,3 +322,84 @@ DEF_TEST(String_fromUTF16, r) {
     REPORTER_ASSERT(r, SkStringFromUTF16(test3, SK_ARRAY_COUNT(test3)).equals("αβγδε ζηθικ"));
 }
 
+static void test_va_list_print(skiatest::Reporter* r, const char format[], ...) {
+    va_list args;
+    va_start(args, format);
+
+    SkString str("123");
+    str.printVAList(format, args);
+    REPORTER_ASSERT(r, str.equals("hello world"));
+
+    va_end(args);
+}
+
+static void test_va_list_append(skiatest::Reporter* r, const char format[], ...) {
+    va_list args;
+    va_start(args, format);
+
+    SkString str("123");
+    str.appendVAList(format, args);
+    REPORTER_ASSERT(r, str.equals("123hello world"));
+
+    va_end(args);
+}
+
+static void test_va_list_prepend(skiatest::Reporter* r, const char format[], ...) {
+    va_list args;
+    va_start(args, format);
+
+    SkString str("123");
+    str.prependVAList(format, args);
+    REPORTER_ASSERT(r, str.equals("hello world123"));
+
+    va_end(args);
+}
+
+DEF_TEST(String_VAList, r) {
+    test_va_list_print(r, "%s %c%c%c%c%c", "hello", 'w', 'o', 'r', 'l', 'd');
+    test_va_list_append(r, "%s %c%c%c%c%c", "hello", 'w', 'o', 'r', 'l', 'd');
+    test_va_list_prepend(r, "%s %c%c%c%c%c", "hello", 'w', 'o', 'r', 'l', 'd');
+}
+
+static void test_va_list_overflow_print(skiatest::Reporter* r, const char format[], ...) {
+    va_list args;
+    va_start(args, format);
+
+    SkString str("X");
+    str.printVAList(format, args);
+    assert_2000_spaces(r, str);
+
+    va_end(args);
+}
+
+static void test_va_list_overflow_append(skiatest::Reporter* r, const char format[], ...) {
+    va_list args;
+    va_start(args, format);
+
+    SkString str("X");
+    str.appendVAList(format, args);
+    REPORTER_ASSERT(r, str[0] == 'X');
+    str[0] = ' ';
+    assert_2000_spaces(r, str);
+
+    va_end(args);
+}
+
+static void test_va_list_overflow_prepend(skiatest::Reporter* r, const char format[], ...) {
+    va_list args;
+    va_start(args, format);
+
+    SkString str("X");
+    str.prependVAList(format, args);
+    REPORTER_ASSERT(r, str[1999] == 'X');
+    str[1999] = ' ';
+    assert_2000_spaces(r, str);
+
+    va_end(args);
+}
+
+DEF_TEST(String_VAList_overflow, r) {
+    test_va_list_overflow_print(r, "%2000s", " ");
+    test_va_list_overflow_append(r, "%1999s", " ");
+    test_va_list_overflow_prepend(r, "%1999s", " ");
+}