[epaper_spi] Ensure test card gets drawn (#20804)

esphome/components/epaper_spi/display.py

@@ -208,6 +208,7 @@ def _final_validate(config) -> None:
         else:
             # If no drawing methods are configured, and LVGL is not enabled, show a test card
             config[CONF_SHOW_TEST_CARD] = True
+            config[CONF_UPDATE_INTERVAL] = update_interval("1min")
     elif CONF_UPDATE_INTERVAL not in config:
         config[CONF_UPDATE_INTERVAL] = update_interval("1min")
 

tests/component_tests/epaper_spi/config/test_card_update_interval.yaml

@@ -0,0 +1,22 @@
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+
+spi:
+  clk_pin: GPIO18
+  mosi_pin: GPIO19
+
+display:
+  - platform: epaper_spi
+    id: epaper_display
+    model: ssd1677
+    dc_pin: GPIO21
+    busy_pin: GPIO22
+    reset_pin: GPIO23
+    cs_pin: GPIO5
+    update_interval: never
+    dimensions:
+      width: 200
+      height: 200

tests/component_tests/epaper_spi/test_init.py

@@ -580,3 +580,15 @@ def test_model_with_no_default_init_sequence_generates(
     # init_sequence_length, ...); a length of 0 confirms the empty init
     # sequence array was generated instead of raising during code generation.
     assert re.search(r"epaper_spi::EPaperT133A01\([^;]*,\s*\w+,\s*0\);", main_cpp)
+
+
+def test_test_card_overrides_update_interval(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """With nothing else to draw, update_interval is not left at never for the test card."""
+    main_cpp = generate_main(component_config_path("test_card_update_interval.yaml"))
+
+    match = re.search(r"epaper_display->set_update_interval\((\d+)\);", main_cpp)
+    assert match is not None
+    assert int(match.group(1)) != 4294967295