e2e-suite-budget

Overview

This skill computes per-test ROI and recommends which tests to retire / move to a lower layer / fix.

When to use

• E2E suite has grown past 50-100 tests.
• CI time is dominated by E2E (slow CI pipeline).
• Flake rate >5%; team is fatigued.
• Team wants to reduce test maintenance burden or decide which tests to remove.
• Quarterly: scheduled budget review.

How to use

1. Gather the E2E inventory - per test, pull runtime, flake rate, regressions caught, maintenance PR count, and a 1-5 value tier (Step 1).
2. Validate inputs - confirm every test has runtime and flake data; flag and exclude gaps (Step 1a).
3. Compute per-test ROI = (regressions caught × value) / (runtime × flake rate × maintenance) (Steps 2-3).
4. Rank every test ascending by ROI and take the bottom decile as the action list (Step 4).
5. Decide per bottom-decile test: retire, move to a lower layer, or fix the flake (Step 5).
6. Enforce the absolute budget - once the suite exceeds the cap, adding a new E2E test must retire an existing one (Step 6).
7. Re-run quarterly, and reactively after any flake spike (Step 7).

Step 1 - Inputs

Per-E2E-test, the agent / skill needs:

• Runtime: average per-test duration (from CI).
• Flake rate: % of CI runs where the test failed then passed on retry (from CI history per junit-xml-analysis in the qa-test-reporting plugin, Step 3).
• Regression-catch count: how many real bugs this test caught in the last N months (from incident postmortems referencing the test, or git-blame on the failing-then-fixed pattern).
• Maintenance cost: PR count modifying the test in last N months (proxy for fragility).
• Value tier: 1-5; assigned by team (5 = critical journey).

Step 1a - Validate inputs

Before scoring, verify data completeness:

• Every test ID present in stats must have a runtime_min value; flag any missing as SKIP - no runtime data.
• Flag any test with a missing or null flake_rate as NEEDS MANUAL REVIEW and exclude from automated scoring until resolved.
• Confirm maintenance and regressions files share the same set of test IDs as stats; log any mismatches.
• Sanity-check the ROI distribution after scoring (Step 3): if >50% of tests score 0.0, the regressions data is likely missing or incomplete - warn before generating recommendations.

Step 2 - ROI formula

ROI = (regressions_caught × value_tier) / (runtime_min × (1 + flake_rate) × (1 + maintenance_count_norm))

Where:

• regressions_caught ≥ 0 (defaults to 0; can be fractional for "caught a near-miss").
• value_tier ∈ [1, 5].
• runtime_min is the test's average runtime in minutes.
• flake_rate ∈ [0, 1] (e.g., 0.05 = 5% flake).
• maintenance_count_norm is PRs touching the test in the window divided by the median for the suite (so a typical-maintenance test has factor ~1).

Higher ROI = more value per cost.

Step 3 - Per-test scoring

# per-test ROI scoring - implements the Step 2 formula
import json, sys
from collections import defaultdict

# Load per-test stats from CI history
stats = json.load(open(sys.argv[1]))  # {test_id: {runtime, flake_rate, ...}}
regressions = json.load(open(sys.argv[2]))  # {test_id: count}
value_tiers = json.load(open(sys.argv[3]))  # {test_id: tier}
maintenance = json.load(open(sys.argv[4]))  # {test_id: pr_count}
median_pr_count = sorted(maintenance.values())[len(maintenance) // 2] or 1

scores = {}
for tid, s in stats.items():
    rc = regressions.get(tid, 0)
    vt = value_tiers.get(tid, 3)
    rt = s['runtime_min']
    fr = s['flake_rate']
    mn = maintenance.get(tid, 0) / median_pr_count
    score = (rc * vt) / (rt * (1 + fr) * (1 + mn))
    scores[tid] = score

# Sort ascending - lowest ROI first
ranked = sorted(scores.items(), key=lambda x: x[1])
print(json.dumps(ranked))

Step 4 - Output: bottom decile

## E2E suite budget - `<repo>` - Q2 2026

**Total E2E tests:** 142
**Total runtime:** 38 min (per CI run)
**Median flake rate:** 4.2%
**Bottom-decile (14 tests) recommended for action:**

| Test                                              | ROI | Runtime | Flake | Regressions caught | Value tier | Recommendation |
|---------------------------------------------------|----:|--------:|------:|-------------------:|-----------:|----------------|
| `archive-flow.spec.ts > old-orders`                | 0.0 |   2.1m  |  18%  |        0           |     2      | Retire - high flake, no signal in 6mo. |
| `legacy-checkout.spec.ts > deprecated-promo`       | 0.1 |   3.2m  |   8%  |        0           |     1      | Retire - feature deprecated. |
| `cart.spec.ts > add 1000 items`                    | 0.2 |   4.5m  |   2%  |        0           |     2      | Move to perf suite - not E2E concern. |
| `e2e-utils.spec.ts > date-formatting`              | 0.5 |   0.8m  |   1%  |        0           |     2      | Move to unit layer. |
| ... (10 more)                                       |     |         |       |                    |            |                |

### Estimated impact of acting on all 14

- Suite size: 142 → 128 (-14)
- Runtime: 38 min → 28 min (-10 min per CI run, ~26% reduction)
- Flake-related reruns: estimated -50%
- Maintenance load: -20% (these 14 had the highest PR-touch count)

Step 5 - Categorize recommendations

The team picks the appropriate class per test; the skill recommends.

Step 6 - Cap discipline

Set an absolute budget:

# e2e-budget.yml
budget:
  max_tests: 100
  max_runtime_min: 30
  max_flake_rate: 0.03   # 3%

When the suite exceeds budget, the next sprint's "add new E2E test" requires retiring / moving an existing one. Force the trade-off.

Step 7 - Cadence

Worked example

A 40-test E2E suite, median maintenance = 2 PRs/quarter (so maintenance_count_norm = PRs ÷ 2). Scoring three representative tests:

The ROI column above is computed with the Step 2 formula. Ranked ascending: dismiss-cookie (0.0) → csv-export (0.21) → guest-purchase (4.9). The bottom decile of 40 is the lowest 4 tests; the first two here fall in it.

Decisions:

• dismiss-cookie → retire: 0 regressions in the window, 20% flake, feature deprecated - pure cost.
• csv-export → lower-layer: catches a real regression but tier-2 value, and CSV formatting is cheaply covered by a unit test; rewrite there.
• guest-purchase → keep: highest ROI in the suite; critical journey, low flake, worth its runtime.

Anti-patterns and Limitations

See references/anti-patterns-and-limitations.md for common failure modes (missing regression data, auto-retiring without review, cherry-picking) and known constraints (difficulty gathering regression-catch data, heuristic formula tuning, "test of last resort" cases, migration cost).

References

• tp - Cohn's pyramid: UI tests "brittle, expensive to write, and time consuming to run."
• test-pyramid-balancer - sibling: identifies the layer-balance issue this skill addresses tactically.
• flaky-test-quarantine - sibling: handles the flake side of low-ROI tests.
• junit-xml-analysis - upstream: provides per-test runtime + flake stats.
• test-coverage-targeter - complementary: identifies what to add at the unit layer when E2E tests get retired.