test: fix remaining environment handling and error message assertions

Process.env preservation fixes:
- Fix destructive process.env = {} in parameter-passthrough.spec.ts
- Fix destructive process.env = {} in edge-cases.spec.ts
- Apply same safe originalEnv pattern used in engine tests
- Preserves PATH, HOME, and system vars; restores in afterAll
- Eliminates environment pollution between test files

Error message assertion fixes:
- Update getRemoteUrl tests to assert against gh-pages v3.2.3 exact errors
- Non-existent remote: "Failed to get remote.{remote}.url (task must...)"
- Not-in-git-repo: Same error format (gh-pages doesn't distinguish)
- Tests now pin actual upstream error contract for upgrade safety

Documentation updates:
- Update TEST_COVERAGE_PLAN.md test safety claim to be accurate
- Changed "process.env properly preserved" to "using originalEnv pattern"

All 351 tests passing. Test suite now honestly ready for gh-pages v6 upgrade.

Author: JohannesHoppe

TEST_COVERAGE_PLAN.md

@@ -223,7 +223,7 @@ All behavioral tests for gh-pages v3.2.3 are now complete and provide comprehens
 - **gh-pages/lib/git:** ✅ Internal API dependency intensively tested (3 focused tests verifying correctness)
 - **Dotfiles:** ✅ Tests verify actual file list differences (4 files with dotfiles, 3 without)
 - **Quality:** ✅ Zero regressions, all tests passing, zero 'any' types (HARD RULE compliant)
-- **Test Safety:** ✅ process.env properly preserved (PATH, HOME, etc.) across all test files
+- **Test Safety:** ✅ process.env properly preserved using originalEnv pattern in all test files
 
 ---
 

src/engine/engine.prepare-options-helpers.spec.ts

@@ -613,10 +613,10 @@ describe('prepareOptions helpers - intensive tests', () => {
         remote: 'nonexistent-remote-12345' // Remote that definitely doesn't exist
       };
 
-      // Should throw with specific error message about the remote
+      // gh-pages v3.2.3 throws this exact error message for non-existent remotes
       await expect(helpers.getRemoteUrl(options))
         .rejects
-        .toThrow('Failed to get remote.');
+        .toThrow('Failed to get remote.nonexistent-remote-12345.url (task must either be run in a git repository with a configured nonexistent-remote-12345 remote or must be configured with the "repo" option).');
     });
 
     it('should throw helpful error when not in a git repository', async () => {
@@ -629,9 +629,10 @@ describe('prepareOptions helpers - intensive tests', () => {
         process.chdir(tempDir);
         const options = { remote: 'origin' };
 
+        // gh-pages v3.2.3 throws this exact error message when not in a git repo
         await expect(helpers.getRemoteUrl(options))
           .rejects
-          .toThrow('run in a git repository');
+          .toThrow('Failed to get remote.origin.url (task must either be run in a git repository with a configured origin remote or must be configured with the "repo" option).');
       } finally {
         process.chdir(originalCwd);
         await require('fs-extra').remove(tempDir);

src/parameter-tests/edge-cases.spec.ts

@@ -18,10 +18,35 @@ import { DeployUser } from '../interfaces';
 
 describe('Edge Case Tests', () => {
   let logger: logging.LoggerApi;
+  const originalEnv = process.env;
 
   beforeEach(() => {
     logger = new logging.NullLogger();
-    process.env = {};
+    // Create fresh copy of environment for each test
+    // This preserves PATH, HOME, etc. needed by git
+    process.env = { ...originalEnv };
+    // Clear only CI-specific vars we're testing
+    delete process.env.TRAVIS;
+    delete process.env.TRAVIS_COMMIT_MESSAGE;
+    delete process.env.TRAVIS_REPO_SLUG;
+    delete process.env.TRAVIS_COMMIT;
+    delete process.env.TRAVIS_BUILD_ID;
+    delete process.env.CIRCLECI;
+    delete process.env.CIRCLE_PROJECT_USERNAME;
+    delete process.env.CIRCLE_PROJECT_REPONAME;
+    delete process.env.CIRCLE_SHA1;
+    delete process.env.CIRCLE_BUILD_URL;
+    delete process.env.GITHUB_ACTIONS;
+    delete process.env.GITHUB_REPOSITORY;
+    delete process.env.GITHUB_SHA;
+    delete process.env.GH_TOKEN;
+    delete process.env.PERSONAL_TOKEN;
+    delete process.env.GITHUB_TOKEN;
+  });
+
+  afterAll(() => {
+    // Restore original environment for other test files
+    process.env = originalEnv;
   });
 
   describe('Empty/null/undefined handling', () => {

src/parameter-tests/parameter-passthrough.spec.ts

@@ -17,10 +17,35 @@ import * as engine from '../engine/engine';
 
 describe('Parameter Passthrough Tests', () => {
   let logger: logging.LoggerApi;
+  const originalEnv = process.env;
 
   beforeEach(() => {
     logger = new logging.NullLogger();
-    process.env = {};
+    // Create fresh copy of environment for each test
+    // This preserves PATH, HOME, etc. needed by git
+    process.env = { ...originalEnv };
+    // Clear only CI-specific vars we're testing
+    delete process.env.TRAVIS;
+    delete process.env.TRAVIS_COMMIT_MESSAGE;
+    delete process.env.TRAVIS_REPO_SLUG;
+    delete process.env.TRAVIS_COMMIT;
+    delete process.env.TRAVIS_BUILD_ID;
+    delete process.env.CIRCLECI;
+    delete process.env.CIRCLE_PROJECT_USERNAME;
+    delete process.env.CIRCLE_PROJECT_REPONAME;
+    delete process.env.CIRCLE_SHA1;
+    delete process.env.CIRCLE_BUILD_URL;
+    delete process.env.GITHUB_ACTIONS;
+    delete process.env.GITHUB_REPOSITORY;
+    delete process.env.GITHUB_SHA;
+    delete process.env.GH_TOKEN;
+    delete process.env.PERSONAL_TOKEN;
+    delete process.env.GITHUB_TOKEN;
+  });
+
+  afterAll(() => {
+    // Restore original environment for other test files
+    process.env = originalEnv;
   });
 
   describe('Parameter: repo', () => {