Add tests for rebase and mixed merge/rebase workflows

.github/workflows/tests.yml

@@ -13,7 +13,10 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Run unit tests
-        run: bash tests/test_update_pr_stack.sh
+        run: |
+          bash tests/test_update_pr_stack.sh
+          bash tests/test_rebase_workflow.sh
+          bash tests/test_mixed_workflows.sh
 
   e2e-tests:
     name: E2E Tests

README.md

@@ -10,7 +10,7 @@ If you use squash & merge instead, your main branch history stays nice and clean
 
 ### The solution
 
-This action tries to fix that in a transparent way. Install it, and hopefully the workflow of stacking + merge during dev + squash merge when landing works.
+This action tries to fix that in a transparent way. Install it, and hopefully the workflow of stacking + merge during dev + squash merge when landing works. It also works if you rebase during development instead of merging.
 
 ---
 

tests/test_mixed_workflows.sh

@@ -0,0 +1,222 @@
+#!/bin/bash
+#
+# Test mixed merge/rebase workflows where feature2 is NOT fully up to date
+# with feature1 at the time of squash-merge.
+#
+# Scenarios:
+#   A) feature2 rebased onto an intermediate state of feature1, then feature1
+#      got more commits that feature2 never picked up.
+#   B) feature2 merged feature1 once, then rebased onto a later feature1 state,
+#      but feature1 got yet more commits after that.
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "$SCRIPT_DIR/../command_utils.sh"
+
+simulate_push() {
+    log_cmd git update-ref "refs/remotes/origin/$1" "$1"
+}
+
+# Extract just the +/- lines from a diff (ignoring headers and context)
+diff_changes() {
+    grep '^[+-]' | grep -v '^[+-][+-][+-]'
+}
+
+run_scenario() {
+    local SCENARIO_NAME="$1"
+    echo ""
+    echo "============================================"
+    echo "  Scenario $SCENARIO_NAME"
+    echo "============================================"
+    echo ""
+
+    TEST_REPO=$(mktemp -d)
+    cd "$TEST_REPO"
+
+    log_cmd git init -b main
+    log_cmd git config user.email "test@example.com"
+    log_cmd git config user.name "Test User"
+
+    # 10-line file to keep changes well-separated
+    for i in $(seq 1 10); do echo "line $i" >> file.txt; done
+    log_cmd git add file.txt
+    log_cmd git commit -m "Initial commit"
+    simulate_push main
+}
+
+assert_diff_is() {
+    local LABEL="$1"
+    local EXPECTED="$2"
+    local ACTUAL
+    ACTUAL=$(log_cmd git diff main...feature2 | diff_changes)
+    if [[ "$ACTUAL" == "$EXPECTED" ]]; then
+        echo "✅ $LABEL"
+    else
+        echo "❌ $LABEL"
+        echo "Expected changed lines:"
+        echo "$EXPECTED"
+        echo "Actual changed lines:"
+        echo "$ACTUAL"
+        exit 1
+    fi
+}
+
+assert_idempotent() {
+    local BEFORE AFTER
+    BEFORE=$(git rev-parse feature2)
+    run_update_pr_stack
+    cd "$TEST_REPO"
+    AFTER=$(git rev-parse feature2)
+    if [[ "$BEFORE" == "$AFTER" ]]; then
+        echo "✅ Idempotent"
+    else
+        echo "❌ Idempotence failed"
+        exit 1
+    fi
+}
+
+squash_merge_feature1() {
+    log_cmd git checkout main
+    log_cmd git merge --squash feature1
+    log_cmd git commit -m "Squash merge feature1"
+    SQUASH_COMMIT=$(git rev-parse HEAD)
+    simulate_push main
+    echo "Squash commit: $SQUASH_COMMIT"
+}
+
+run_update_pr_stack() {
+    log_cmd \
+      env \
+      SQUASH_COMMIT=$SQUASH_COMMIT \
+      MERGED_BRANCH=feature1 \
+      TARGET_BRANCH=main \
+      GH="$SCRIPT_DIR/mock_gh.sh" \
+      GIT="$SCRIPT_DIR/mock_git.sh" \
+      $SCRIPT_DIR/../update-pr-stack.sh
+}
+
+########################################################################
+# Scenario A: rebase onto intermediate feature1, then feature1 advances
+########################################################################
+run_scenario "A: rebased onto intermediate feature1, then feature1 advances"
+
+# feature1: two commits (lines 2 and 3)
+log_cmd git checkout -b feature1
+sed -i '2s/.*/f1 commit 1/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "f1: commit 1"
+simulate_push feature1
+
+# feature2: branched from feature1 after commit 1, changes line 9
+log_cmd git checkout -b feature2
+sed -i '9s/.*/f2 content/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "f2: change line 9"
+simulate_push feature2
+
+# feature1 gets commit 2
+log_cmd git checkout feature1
+sed -i '3s/.*/f1 commit 2/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "f1: commit 2"
+simulate_push feature1
+
+# Developer rebases feature2 onto feature1 (picks up commit 2)
+log_cmd git checkout feature2
+log_cmd git rebase feature1
+simulate_push feature2
+
+# feature1 gets commit 3 — feature2 does NOT pick this up
+log_cmd git checkout feature1
+sed -i '4s/.*/f1 commit 3/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "f1: commit 3"
+simulate_push feature1
+
+echo ""
+echo "=== Graph before squash-merge ==="
+log_cmd git log --graph --oneline --all
+echo ""
+
+squash_merge_feature1
+run_update_pr_stack
+cd "$TEST_REPO"
+
+# The diff should show only feature2's unique change
+assert_diff_is "Scenario A: diff shows only f2's change" "$(cat <<'EOF'
+-line 9
++f2 content
+EOF
+)"
+assert_idempotent
+
+########################################################################
+# Scenario B: merge then rebase, then feature1 advances again
+########################################################################
+run_scenario "B: merge then rebase, then feature1 advances again"
+
+# feature1: commit 1 (line 2)
+log_cmd git checkout -b feature1
+sed -i '2s/.*/f1 commit 1/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "f1: commit 1"
+simulate_push feature1
+
+# feature2 from feature1, changes line 9
+log_cmd git checkout -b feature2
+sed -i '9s/.*/f2 content/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "f2: change line 9"
+simulate_push feature2
+
+# feature1 gets commit 2
+log_cmd git checkout feature1
+sed -i '3s/.*/f1 commit 2/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "f1: commit 2"
+simulate_push feature1
+
+# Developer merges feature1 into feature2
+log_cmd git checkout feature2
+log_cmd git merge --no-edit feature1
+simulate_push feature2
+
+# feature1 gets commit 3
+log_cmd git checkout feature1
+sed -i '4s/.*/f1 commit 3/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "f1: commit 3"
+simulate_push feature1
+
+# Developer rebases feature2 onto latest feature1 (rewrite away the merge)
+log_cmd git checkout feature2
+log_cmd git rebase feature1
+simulate_push feature2
+
+# feature1 gets commit 4 — feature2 does NOT pick this up
+log_cmd git checkout feature1
+sed -i '5s/.*/f1 commit 4/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "f1: commit 4"
+simulate_push feature1
+
+echo ""
+echo "=== Graph before squash-merge ==="
+log_cmd git log --graph --oneline --all
+echo ""
+
+squash_merge_feature1
+run_update_pr_stack
+cd "$TEST_REPO"
+
+assert_diff_is "Scenario B: diff shows only f2's change" "$(cat <<'EOF'
+-line 9
++f2 content
+EOF
+)"
+assert_idempotent
+
+########################################################################
+echo ""
+echo "All mixed-workflow tests passed! 🎉"

tests/test_rebase_workflow.sh

@@ -0,0 +1,142 @@
+#!/bin/bash
+#
+# Test that the update-pr-stack mechanism works when PRs are rebased during
+# development (as opposed to using merge commits to sync with the parent).
+#
+# Scenario:
+#   1. main ← feature1 ← feature2 (linear stack)
+#   2. feature1 gets an additional commit AFTER feature2 was branched
+#   3. Developer rebases feature2 onto the updated feature1
+#   4. feature1 is squash-merged into main
+#   5. Action runs → feature2 should get a correct PR diff against main
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "$SCRIPT_DIR/../command_utils.sh"
+
+simulate_push() {
+    local branch_name="$1"
+    log_cmd git update-ref "refs/remotes/origin/$branch_name" "$branch_name"
+}
+
+TEST_REPO=$(mktemp -d)
+cd "$TEST_REPO"
+echo "Created test repo at $TEST_REPO"
+
+log_cmd git init -b main
+log_cmd git config user.email "test@example.com"
+log_cmd git config user.name "Test User"
+
+# Initial commit on main — use enough lines to avoid adjacent-change conflicts
+for i in $(seq 1 10); do echo "line $i" >> file.txt; done
+log_cmd git add file.txt
+log_cmd git commit -m "Initial commit"
+simulate_push main
+
+# feature1: modify line 2 (top region)
+log_cmd git checkout -b feature1
+sed -i '2s/.*/Feature 1 first change/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "feature1: first commit"
+simulate_push feature1
+
+# feature2: branched from feature1, modify line 9 (bottom region, far away)
+log_cmd git checkout -b feature2
+sed -i '9s/.*/Feature 2 content/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "feature2: change line 9"
+simulate_push feature2
+
+# Now feature1 gets an additional commit modifying line 3 (still top region)
+log_cmd git checkout feature1
+sed -i '3s/.*/Feature 1 second change/' file.txt
+log_cmd git add file.txt
+log_cmd git commit -m "feature1: second commit"
+simulate_push feature1
+
+FEATURE1_TIP=$(git rev-parse HEAD)
+
+# Developer rebases feature2 onto the updated feature1
+log_cmd git checkout feature2
+log_cmd git rebase feature1
+simulate_push feature2
+
+echo ""
+echo "=== State before squash-merge ==="
+log_cmd git log --graph --oneline --all
+echo ""
+
+# Squash-merge feature1 into main (simulated via cherry-pick --no-commit + commit)
+log_cmd git checkout main
+# Use merge --squash to properly squash all of feature1's commits
+log_cmd git merge --squash feature1
+log_cmd git commit -m "Squash merge feature1"
+SQUASH_COMMIT=$(git rev-parse HEAD)
+simulate_push main
+
+echo ""
+echo "Squash commit: $SQUASH_COMMIT"
+echo ""
+
+# Run the action
+run_update_pr_stack() {
+  log_cmd \
+    env \
+    SQUASH_COMMIT=$SQUASH_COMMIT \
+    MERGED_BRANCH=feature1 \
+    TARGET_BRANCH=main \
+    GH="$SCRIPT_DIR/mock_gh.sh" \
+    GIT="$SCRIPT_DIR/mock_git.sh" \
+    $SCRIPT_DIR/../update-pr-stack.sh
+}
+run_update_pr_stack
+
+cd "$TEST_REPO"
+
+# Verify: squash commit is an ancestor of feature2
+if log_cmd git merge-base --is-ancestor "$SQUASH_COMMIT" feature2; then
+    echo "✅ feature2 includes the squash commit"
+else
+    echo "❌ feature2 does not include the squash commit"
+    log_cmd git log --graph --oneline --all
+    exit 1
+fi
+
+# Verify: triple-dot diff main...feature2 shows ONLY feature2's unique change
+# We expect the diff to show only feature2's unique change (line 9).
+# Strip index lines and hunk header function-name context for stable comparison.
+EXPECTED_DIFF=$(cat <<'EOF'
+-line 9
++Feature 2 content
+EOF
+)
+ACTUAL_DIFF=$(log_cmd git diff main...feature2 | grep '^[+-]' | grep -v '^[+-][+-][+-]')
+if [[ "$ACTUAL_DIFF" == "$EXPECTED_DIFF" ]]; then
+    echo "✅ Triple-dot diff main...feature2 shows only feature2's unique changes"
+else
+    echo "❌ Triple-dot diff is wrong"
+    echo "Expected:"
+    echo "$EXPECTED_DIFF"
+    echo "Actual:"
+    echo "$ACTUAL_DIFF"
+    diff <(echo "$EXPECTED_DIFF") <(echo "$ACTUAL_DIFF") || true
+    exit 1
+fi
+
+# Verify idempotence
+FEATURE2_BEFORE=$(git rev-parse feature2)
+run_update_pr_stack
+cd "$TEST_REPO"
+FEATURE2_AFTER=$(git rev-parse feature2)
+
+if [[ "$FEATURE2_BEFORE" == "$FEATURE2_AFTER" ]]; then
+    echo "✅ Idempotence: re-running produces no new commits"
+else
+    echo "❌ Idempotence failed"
+    exit 1
+fi
+
+echo ""
+echo "All rebase-workflow tests passed! 🎉"
+echo "Test repository remains at: $TEST_REPO for inspection"