[number] Fix the default mode check so mode auto is no longer emitted (#19231)

tests/component_tests/number/config/mode.yaml

@@ -0,0 +1,28 @@
+---
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+
+number:
+  - platform: template
+    id: auto_number
+    min_value: 0
+    max_value: 10
+    step: 1
+    optimistic: true
+  - platform: template
+    id: box_number
+    min_value: 0
+    max_value: 10
+    step: 1
+    mode: box
+    optimistic: true
+  - platform: template
+    id: explicit_auto_number
+    min_value: 0
+    max_value: 10
+    step: 1
+    mode: auto
+    optimistic: true

tests/component_tests/number/test_number.py

@@ -0,0 +1,16 @@
+"""Tests for the number component codegen."""
+
+from collections.abc import Callable
+from pathlib import Path
+
+
+def test_default_mode_is_not_emitted(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """Mode auto is the C++ initializer, so only a non default mode is set."""
+    main_cpp = generate_main(component_config_path("mode.yaml"))
+
+    assert "auto_number->traits.set_mode(" not in main_cpp
+    assert "explicit_auto_number->traits.set_mode(" not in main_cpp
+    assert "box_number->traits.set_mode(number::NUMBER_MODE_BOX);" in main_cpp