Add demo integration (#2085)

esphome/components/demo/demo_number.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/number/number.h"
+
+namespace esphome {
+namespace demo {
+
+enum class DemoNumberType {
+  TYPE_1,
+  TYPE_2,
+  TYPE_3,
+};
+
+class DemoNumber : public number::Number, public Component {
+ public:
+  void set_type(DemoNumberType type) { type_ = type; }
+  void setup() override {
+    switch (type_) {
+      case DemoNumberType::TYPE_1:
+        this->publish_state(50);
+        break;
+      case DemoNumberType::TYPE_2:
+        this->publish_state(-10);
+        break;
+      case DemoNumberType::TYPE_3:
+        this->publish_state(42);
+        break;
+    }
+  }
+
+ protected:
+  void control(float value) override { this->publish_state(value); }
+
+  DemoNumberType type_;
+};
+
+}  // namespace demo
+}  // namespace esphome