add float list and unit tests

ml-agents-envs/mlagents_envs/side_channel/side_channel.py

     def write_float32(self, f: float) -> None:
         self.buffer += struct.pack("<f", f)
 
+    def write_float32_list(self, float_list: List[float]) -> None:
+        self.write_int32(len(float_list))
+        for f in float_list:
+            self.write_float32(f)
+
     def write_string(self, s: str) -> None:
         encoded_key = s.encode("ascii")
         self.write_int32(len(encoded_key))
         val = struct.unpack_from("<f", self.buffer, self.offset)[0]
         self.offset += 4
         return val
+
+    def read_float32_list(self) -> List[float]:
+        list_len = self.read_int32()
+        output = []
+        for _ in range(list_len):
+            output.append(self.read_float32())
+        return output
 
     def read_string(self) -> str:
         encoded_str_len = self.read_int32()

ml-agents-envs/mlagents_envs/tests/test_side_channel.py

 
     messages = receiver.get_and_clear_received_messages()
     assert len(messages) == 0
+
+
+def test_message_int32():
+    val = 1337
+    msg_out = OutgoingMessage()
+    msg_out.write_int32(val)
+
+    msg_in = IncomingMessage(msg_out.buffer)
+    read_val = msg_in.read_int32()
+    assert val == read_val
+
+
+def test_message_float32():
+    val = 42.0
+    msg_out = OutgoingMessage()
+    msg_out.write_float32(val)
+
+    msg_in = IncomingMessage(msg_out.buffer)
+    read_val = msg_in.read_float32()
+    # These won't be exactly equal in general, since python floats are 64-bit.
+    assert val == read_val
+
+
+def test_message_string():
+    val = "mlagents!"
+    msg_out = OutgoingMessage()
+    msg_out.write_string(val)
+
+    msg_in = IncomingMessage(msg_out.buffer)
+    read_val = msg_in.read_string()
+    assert val == read_val
+
+
+def test_message_float_list():
+    val = [1.0, 3.0, 9.0]
+    msg_out = OutgoingMessage()
+    msg_out.write_float32_list(val)
+
+    msg_in = IncomingMessage(msg_out.buffer)
+    read_val = msg_in.read_float32_list()
+    # These won't be exactly equal in general, since python floats are 64-bit.
+    assert val == read_val