Add comprehensive ERT test suite and fix critical bugs

Session 1: Testing infrastructure and initial test coverage

Bug fixes in wttrin.el:
- Fix wttrin-additional-url-params to handle nil unit system
- Remove incorrect callback parameter to url-retrieve-synchronously
- Add nil buffer check for network failures
- Strip HTTP headers before decoding response
- Kill buffer after fetch to prevent memory leaks
- Fix double concatenation of URL params in cache function
- Add proper URL encoding via new wttrin--build-url function

Refactoring:
- Extract wttrin--build-url as pure, testable function
- Separate URL building logic from network I/O

Test infrastructure (33 tests, 100% passing):
- tests/testutil-wttrin.el: Shared test utilities
- tests/test-wttrin-additional-url-params.el: 7 tests
- tests/test-wttrin--make-cache-key.el: 9 tests
- tests/test-wttrin--build-url.el: 10 tests
- tests/test-wttrin--cleanup-cache-if-needed.el: 7 tests

Documentation:
- docs/testing-plan.org: Comprehensive testing roadmap
- docs/bugs.org: Bug analysis from code review
- docs/NOTES.org: Session tracking and guidelines
- docs/session-1-summary.org: Detailed session summary

Next session: Cache workflow tests, parsing logic extraction, integration tests

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

1 files changed, 69 insertions, 0 deletions

diff --git a/tests/test-wttrin--make-cache-key.el b/tests/test-wttrin--make-cache-key.el
new file mode 100644
index 0000000..442c548
--- /dev/null
+++ b/tests/test-wttrin--make-cache-key.el
@@ -0,0 +1,69 @@
+;;; test-wttrin--make-cache-key.el --- Tests for wttrin--make-cache-key -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2025 Craig Jennings
+
+;;; Commentary:
+
+;; Unit tests for wttrin--make-cache-key function.
+;; Tests cache key generation from location and unit system.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin)
+(require 'testutil-wttrin)
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin--make-cache-key-normal-location-with-metric-returns-key ()
+  "Test that location with metric unit system creates correct cache key."
+  (testutil-wttrin-with-unit-system "m"
+    (should (equal "Paris|m" (wttrin--make-cache-key "Paris")))))
+
+(ert-deftest test-wttrin--make-cache-key-normal-location-with-uscs-returns-key ()
+  "Test that location with USCS unit system creates correct cache key."
+  (testutil-wttrin-with-unit-system "u"
+    (should (equal "New York|u" (wttrin--make-cache-key "New York")))))
+
+(ert-deftest test-wttrin--make-cache-key-normal-location-no-unit-returns-default ()
+  "Test that location with no unit system uses default in cache key."
+  (testutil-wttrin-with-unit-system nil
+    (should (equal "London|default" (wttrin--make-cache-key "London")))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin--make-cache-key-boundary-empty-location-returns-key ()
+  "Test that empty location string creates cache key."
+  (testutil-wttrin-with-unit-system "m"
+    (should (equal "|m" (wttrin--make-cache-key "")))))
+
+(ert-deftest test-wttrin--make-cache-key-boundary-location-with-spaces-returns-key ()
+  "Test that location with spaces creates correct cache key."
+  (testutil-wttrin-with-unit-system "m"
+    (should (equal "New York, NY|m" (wttrin--make-cache-key "New York, NY")))))
+
+(ert-deftest test-wttrin--make-cache-key-boundary-location-with-commas-returns-key ()
+  "Test that location with commas creates correct cache key."
+  (testutil-wttrin-with-unit-system nil
+    (should (equal "Berlin, DE|default" (wttrin--make-cache-key "Berlin, DE")))))
+
+(ert-deftest test-wttrin--make-cache-key-boundary-unicode-location-returns-key ()
+  "Test that Unicode location creates correct cache key."
+  (testutil-wttrin-with-unit-system "m"
+    (should (equal "東京|m" (wttrin--make-cache-key "東京")))))
+
+(ert-deftest test-wttrin--make-cache-key-boundary-location-with-special-chars-returns-key ()
+  "Test that location with special characters creates cache key."
+  (testutil-wttrin-with-unit-system "m"
+    (should (equal "~Eiffel+Tower|m" (wttrin--make-cache-key "~Eiffel+Tower")))))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin--make-cache-key-error-nil-location-returns-key ()
+  "Test that nil location creates cache key with empty string."
+  ;; Note: concat converts nil to empty string, this documents current behavior
+  (testutil-wttrin-with-unit-system "m"
+    (should (equal "|m" (wttrin--make-cache-key nil)))))
+
+(provide 'test-wttrin--make-cache-key)
+;;; test-wttrin--make-cache-key.el ends here