[tests] Add unit test coverage for web_port property

[bdraco]

What does this implement/fix?

Adds unit test coverage for the CORE.web_port property to prevent future regressions that would break the Dashboard's VISIT button functionality.

Background

The Dashboard PR esphome/dashboard#826 fixes Dashboard Issue esphome/dashboard#766 by changing the VISIT button visibility logic from checking loaded_integrations to checking web_port:

# Before (incorrect):
if "web_server" in device.loaded_integrations:
    show_visit_button()

# After (correct):
if device.web_port is not None:
    show_visit_button()

The issue occurred because captive_portal auto-loads ota.web_server platform, causing "web_server" to appear in loaded_integrations even when no web UI is configured.

What This PR Does

This PR adds 4 unit tests in tests/unit_tests/test_core.py to ensure the web_port property behavior remains correct:

1. test_web_port__none - Returns None when no web_server configured
2. test_web_port__explicit_web_server_default_port - Returns 80 when web_server configured without port
3. test_web_port__explicit_web_server_custom_port - Returns custom port when explicitly set
4. test_web_port__ota_web_server_platform_only - Critical - Returns None when only ota.web_server platform is loaded (not full web_server component)

The critical test (#4) ensures that web_port stays None even when:

• "web_server" appears in loaded_integrations (due to platform load)
• "ota/web_server" appears in loaded_platforms
• But CONF_WEB_SERVER is NOT in config (no web UI)

This guarantees the Dashboard fix works correctly.

Implementation Details

The web_port property (in esphome/core/__init__.py:652-662) correctly checks CONF_WEB_SERVER in self.config, which is the explicit user configuration, NOT loaded_integrations:

@property
def web_port(self) -> int | None:
    if self.config is None:
        raise ValueError("Config has not been loaded yet")

    if CONF_WEB_SERVER in self.config:  # ← Checks explicit config
        try:
            return self.config[CONF_WEB_SERVER][CONF_PORT]
        except KeyError:
            return 80

    return None

These tests ensure this behavior never changes accidentally.

Types of changes

• Code quality improvements to existing code or addition of tests

Related issue or feature (if applicable):

• Related to ESPHome Builder displays VISIT for non web server devices dashboard#766
• Prevents regression of Fix VISIT button showing for devices without web_server configured dashboard#826

Test Environment

Not applicable - these are unit tests that run in CI for all platforms.

Example entry for config.yaml:

Not applicable - no user-facing changes.

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs. (Not applicable - no user-facing changes)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.43%. Comparing base (2a16653) to head (92c268a).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #11811      +/-   ##
==========================================
+ Coverage   72.38%   72.43%   +0.05%     
==========================================
  Files          53       53              
  Lines       11134    11134              
  Branches     1504     1504              
==========================================
+ Hits         8059     8065       +6     
+ Misses       2684     2677       -7     
- Partials      391      392       +1     

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[Copilot]

Pull Request Overview

This PR adds comprehensive unit test coverage for the web_port property in the EsphomeCore class. The tests validate the correct behavior of web port detection and specifically address Dashboard Issue #766 regarding the distinction between the OTA web_server platform and the full web_server component.

• Added tests for web_port property covering multiple scenarios
• Included critical test case for OTA web_server platform edge case
• Comprehensive documentation explaining the Dashboard Issue #766 context

[bdraco]

Thanks