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, 60 insertions, 0 deletions

diff --git a/tests/test-wttrin-additional-url-params.el b/tests/test-wttrin-additional-url-params.el
new file mode 100644
index 0000000..60918a4
--- /dev/null
+++ b/tests/test-wttrin-additional-url-params.el
@@ -0,0 +1,60 @@
+;;; test-wttrin-additional-url-params.el --- Tests for wttrin-additional-url-params -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2025 Craig Jennings
+
+;;; Commentary:
+
+;; Unit tests for wttrin-additional-url-params function.
+;; Tests URL parameter generation with different unit system configurations.
+
+;;; Code:
+
+(require 'ert)
+(require 'wttrin)
+(require 'testutil-wttrin)
+
+;;; Normal Cases
+
+(ert-deftest test-wttrin-additional-url-params-normal-metric-returns-param ()
+  "Test that metric unit system returns ?m parameter."
+  (testutil-wttrin-with-unit-system "m"
+    (should (equal "?m" (wttrin-additional-url-params)))))
+
+(ert-deftest test-wttrin-additional-url-params-normal-uscs-returns-param ()
+  "Test that USCS unit system returns ?u parameter."
+  (testutil-wttrin-with-unit-system "u"
+    (should (equal "?u" (wttrin-additional-url-params)))))
+
+(ert-deftest test-wttrin-additional-url-params-normal-wind-speed-returns-param ()
+  "Test that wind speed unit returns ?M parameter."
+  (testutil-wttrin-with-unit-system "M"
+    (should (equal "?M" (wttrin-additional-url-params)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-wttrin-additional-url-params-boundary-nil-returns-question-mark ()
+  "Test that nil unit system returns just ? parameter."
+  (testutil-wttrin-with-unit-system nil
+    (should (equal "?" (wttrin-additional-url-params)))))
+
+(ert-deftest test-wttrin-additional-url-params-boundary-empty-string-returns-question-mark ()
+  "Test that empty string unit system returns just ? parameter."
+  (testutil-wttrin-with-unit-system ""
+    (should (equal "?" (wttrin-additional-url-params)))))
+
+(ert-deftest test-wttrin-additional-url-params-boundary-single-char-returns-param ()
+  "Test that single character unit system returns ?<char> parameter."
+  (testutil-wttrin-with-unit-system "x"
+    (should (equal "?x" (wttrin-additional-url-params)))))
+
+;;; Error Cases
+
+(ert-deftest test-wttrin-additional-url-params-error-number-signals-error ()
+  "Test that number unit system signals a type error."
+  ;; concat requires string or sequence, number causes wrong-type-argument error
+  (testutil-wttrin-with-unit-system 123
+    (should-error (wttrin-additional-url-params)
+                  :type 'wrong-type-argument)))
+
+(provide 'test-wttrin-additional-url-params)
+;;; test-wttrin-additional-url-params.el ends here