diff --git a/lib/std/core/conv.c3 b/lib/std/core/conv.c3
index bd563abca..b839893db 100644
--- a/lib/std/core/conv.c3
+++ b/lib/std/core/conv.c3
@@ -104,24 +104,28 @@ fn void! char16_to_utf8_unsafe(Char16 *ptr, usz *available, char** output)
  * @param c `The utf32 codepoint to convert`
  * @param [inout] output `the resulting buffer`
  **/
-fn void char32_to_utf8_unsafe(Char32 c, char** output)
+fn usz char32_to_utf8_unsafe(Char32 c, char** output)
 {
-	switch (true)
+	switch
 	{
 		case c < 0x7f:
 			(*output)++[0] = (char)c;
+			return 1;
 		case c < 0x7ff:
 			(*output)++[0] = (char)(0xC0 | c >> 6);
 			(*output)++[0] = (char)(0x80 | (c & 0x3F));
+			return 2;
 		case c < 0xffff:
 			(*output)++[0] = (char)(0xE0 | c >> 12);
 			(*output)++[0] = (char)(0x80 | (c >> 6 & 0x3F));
 			(*output)++[0] = (char)(0x80 | (c & 0x3F));
+			return 3;
 		default:
 			(*output)++[0] = (char)(0xF0 | c >> 18);
 			(*output)++[0] = (char)(0x80 | (c >> 12 & 0x3F));
 			(*output)++[0] = (char)(0x80 | (c >> 6 & 0x3F));
 			(*output)++[0] = (char)(0x80 | (c & 0x3F));
+			return 4;
 	}
 }
 
diff --git a/lib/std/core/dstring.c3 b/lib/std/core/dstring.c3
index cbac0991f..c3f3657b5 100644
--- a/lib/std/core/dstring.c3
+++ b/lib/std/core/dstring.c3
@@ -136,8 +136,7 @@ fn void DString.append_char32(&self, Char32 c)
 {
 	char[4] buffer @noinit;
 	char* p = &buffer;
-	conv::char32_to_utf8_unsafe(c, &p);
-	usz n = p - (char*)&buffer;
+	usz n = conv::char32_to_utf8_unsafe(c, &p);
 	self.reserve(n);
 	StringData* data = self.data();
 	data.chars[data.len:n] = buffer[:n];
diff --git a/lib/std/io/formatter_private.c3 b/lib/std/io/formatter_private.c3
index 3235e38b5..df375ae34 100644
--- a/lib/std/io/formatter_private.c3
+++ b/lib/std/io/formatter_private.c3
@@ -11,15 +11,17 @@ fn usz! Formatter.adjust(&self, usz len) @local
 
 fn uint128! int_from_any(any* arg, bool *is_neg) @private
 {
+	switch (arg.type.kindof)
+	{
+		case TypeKind.POINTER:
+			*is_neg = false;
+			return (uint128)(uptr)*(void**)arg.ptr;
+		case TypeKind.DISTINCT:
+		case TypeKind.ENUM:
+			return int_from_any(arg.as_inner(), is_neg);
+		default:
+	}
 	*is_neg = false;
-	if (arg.type.kindof == TypeKind.POINTER)
-	{
-		return (uint128)(uptr)*(void**)arg.ptr;
-	}
-	if (arg.type.kindof == TypeKind.DISTINCT)
-	{
-		return int_from_any(arg.as_inner(), is_neg);
-	}
 	switch (arg)
 	{
 		case bool:
diff --git a/test/unit/stdlib/core/dstring.c3 b/test/unit/stdlib/core/dstring.c3
index b8cfb879b..fe9924379 100644
--- a/test/unit/stdlib/core/dstring.c3
+++ b/test/unit/stdlib/core/dstring.c3
@@ -1,4 +1,128 @@
-module std::core::dstring::tests @test;
+module std::core::dstring2 @test;
+
+const TEST_STRING = "hello world";
+
+fn void test_append()
+{
+	DString str = dstring::new(TEST_STRING);
+	defer str.free();
+	String s;
+
+	assert(str.len() == TEST_STRING.len);
+	assert(str.capacity() == 16);
+
+	s = str.str_view();
+	assert(s == TEST_STRING, "got '%s'; want '%s'", s, TEST_STRING);
+	ZString zs;
+	zs = str.zstr_view();
+	assert(s.ptr[s.len] == 0, "got '%c'; want 0", s.ptr[s.len]);
+
+	str.chop(5);
+	s = str.str_view();
+	assert(s == TEST_STRING[:5], "got '%s'; want '%s'", s, TEST_STRING[:5]);
+
+	str.append(TEST_STRING[5..]);
+	s = str.str_view();
+	assert(s == TEST_STRING, "got '%s'; want '%s'", s, TEST_STRING);
+
+	str.append_char('x');
+	s = str.str_view();
+	assert(s[^1] == 'x', "got '%c'; want 'x'", s[^1]);
+
+	str.append('y');
+	s = str.str_view();
+	assert(s[^1] == 'y', "got '%c'; want 'y'", s[^1]);
+
+	str.set(0, 'z');
+	s = str.str_view();
+	assert(s[0] == 'z', "got '%c'; want 'z'", s[0]);
+
+	str.clear();
+	assert(str.len() == 0);
+
+	str.append_char32('é');
+	s = str.str_view();
+	assert(s == "é", "got '%s'; want 'é'", s);
+
+	str.append_utf32({ 'è', 'à' });
+	s = str.str_view();
+	assert(s == "éèà", "got '%s'; want 'éèà'", s);
+	str.clear();
+
+	str.append_chars("foo");
+	s = str.str_view();
+	assert(s == "foo", "got '%s'; want 'foo'", s);
+	str.clear();
+
+	str.append_repeat('x', 3);
+	s = str.str_view();
+	assert(s == "xxx", "got '%s'; want 'xxx'", s);
+
+	DString str2 = dstring::new("yyy");
+	defer str2.free();
+	DString str3 = str.new_concat(str2);
+	defer str3.free();
+	s = str3.str_view();
+	assert(s == "xxxyyy", "got '%s'; want 'xxxyyy'", s);
+
+	str3.clear();
+	str3.append_string(str2);
+	s = str3.str_view();
+	assert(s == "yyy", "got '%s'; want 'yyy'", s);
+}
+
+fn void test_print()
+{
+	DString str = dstring::new("");
+	defer str.free();
+	String s;
+
+	str.printf("_%s_", "foo");
+	s = str.str_view();
+	assert(s == "_foo_", "got '%s'; want '_foo_'", s);
+
+	str.clear();
+	str.printfn("_%s_", "foo");
+	s = str.str_view();
+	assert(s == "_foo_\n", "got '%s'; want '_foo_\n'", s);
+}
+
+fn void test_copy()
+{
+	DString str = dstring::new(TEST_STRING);
+	defer str.free();
+	String s;
+
+	DString str2 = str.copy();
+	defer str2.free();
+	s = str2.str_view();
+	assert(s == TEST_STRING, "got '%s'; want '%s'", s, TEST_STRING);
+}
+
+fn void test_cmp()
+{
+	DString str = dstring::new(TEST_STRING);
+	defer str.free();
+
+	DString str2 = dstring::new(TEST_STRING);
+	defer str2.free();
+
+	assert(str.equals(str2));
+
+	str2.clear();
+	str2.append("hello you..");
+	assert(str.len() == str2.len());
+	assert(!str.less(str2));
+}
+
+fn void test_join()
+{
+	DString str = dstring::new_join({"hello", "world"}, " ");
+	defer str.free();
+
+	String s = str.str_view();
+	assert(s == TEST_STRING, "got '%s'; want '%s'", s, TEST_STRING);
+}
 
 fn void test_insert_at()
 {
diff --git a/test/unit/stdlib/io/printf.c3 b/test/unit/stdlib/io/printf.c3
index 302bb03c9..445a7104e 100644
--- a/test/unit/stdlib/io/printf.c3
+++ b/test/unit/stdlib/io/printf.c3
@@ -50,4 +50,25 @@ fn void printf_a()
 	String ss = "hello world";
 	s = string::printf("%.4s %.5s", ss, ss);
 	assert(s == "hell hello", "got '%s'; want 'hell hello'", s);
+}
+
+enum PrintfTest : ushort
+{
+	ENUMA,
+	ENUMB,
+}
+
+fn void printf_enum()
+{
+	String s;
+
+	s = string::printf("%s", PrintfTest.ENUMA);
+	assert(s == "ENUMA", "got '%s'; want 'ENUMA'", s);
+	s = string::printf("%s", PrintfTest.ENUMB);
+	assert(s == "ENUMB", "got '%s'; want 'ENUMB'", s);
+
+	s = string::printf("%d", PrintfTest.ENUMA);
+	assert(s == "0", "got '%s'; want '0'", s);
+	s = string::printf("%d", PrintfTest.ENUMB);
+	assert(s == "1", "got '%s'; want '1'", s);
 }
\ No newline at end of file