Create a unit7 for all unit tests.

test/unit7/stdlib/io/bytebuffer.c3

@@ -0,0 +1,29 @@
+module std::io::bytebuffer @test;
+import std::io;
+
+fn void write_read()
+{
+	ByteBuffer buffer;
+	buffer.new_init(0);
+	defer buffer.free();
+	buffer.write("hello")!!;
+
+	char[8] bytes;
+	usz n = buffer.read(bytes[..])!!;
+	assert(n == 5);
+	assert((String)bytes[:n] == "hello");
+
+	buffer.write("hello world")!!;
+	n = buffer.read(bytes[..])!!;
+	assert(n == bytes.len);
+	assert((String)bytes[:n] == "hello wo");
+	assert(buffer.read_idx == 1);
+
+	char c = buffer.read_byte()!!;
+	assert(c == 'r');
+	buffer.pushback_byte()!!;
+
+	n = buffer.read(bytes[..])!!;
+	assert((String)bytes[:n] == "rld");
+	assert(buffer.read_idx == 1);
+}