[uart] Share uart_tcp's write pacing and uart_id matcher (#20464)

tests/components/uart/uart_paced_write_room.cpp

@@ -0,0 +1,62 @@
+#include <cstdint>
+
+#include "common.h"
+#include "esphome/core/application.h"
+
+namespace esphome::uart::testing {
+
+class RoomUART : public MockUARTComponent {
+ public:
+  size_t available_for_write() override { return this->room; }
+  size_t room{SIZE_MAX};
+};
+
+class PacedWriteRoom : public ::testing::Test {
+ protected:
+  void SetUp() override {
+    App.set_loop_interval(16);
+    this->uart_.set_baud_rate(9600);
+  }
+  void TearDown() override {
+    App.set_loop_interval(16);
+    this->at_(0);
+  }
+  // Publishes now_ms as the loop start time, as Application::loop() does.
+  void at_(uint32_t now_ms) { LoopBlockingGuard dispatch{nullptr, nullptr, now_ms}; }
+
+  RoomUART uart_;
+};
+
+TEST_F(PacedWriteRoom, KnownRoomIsReturned) {
+  this->uart_.room = 7;
+  this->at_(1000);
+  EXPECT_EQ(this->uart_.paced_write_room(0), 7u);
+  this->uart_.room = 0;
+  EXPECT_EQ(this->uart_.paced_write_room(0), 0u);
+}
+
+TEST_F(PacedWriteRoom, UnknownRoomTakesOneLoopInterval) {
+  this->at_(1000);
+  // 9600 baud at 10 bits per byte for 16 ms.
+  EXPECT_EQ(this->uart_.paced_write_room(0), 15u);
+}
+
+TEST_F(PacedWriteRoom, EarlyPassTakesTheTimeSinceTheLastWrite) {
+  this->at_(1005);
+  EXPECT_EQ(this->uart_.paced_write_room(1000), 4u);
+}
+
+TEST_F(PacedWriteRoom, AtLeastOneByte) {
+  this->at_(1000);
+  EXPECT_EQ(this->uart_.paced_write_room(1000), 1u);
+}
+
+TEST_F(PacedWriteRoom, SpanCapsAtFourSeconds) {
+  App.set_loop_interval(10000);
+  this->uart_.set_baud_rate(300);
+  this->at_(6000);
+  // 30 bytes/s for 4 s.
+  EXPECT_EQ(this->uart_.paced_write_room(0), 120u);
+}
+
+}  // namespace esphome::uart::testing