Add property/fuzz/invariant tests; fix 2 fuzz-found bugs; restore Makefile (#152)

.github/workflows/build.yml

@@ -28,11 +28,11 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v6
       - name: Build
-        run: go build -mod=readonly ./...
+        run: make build
       - name: Verify
         run: go mod verify
       - name: Test
-        run: env "GORACE=halt_on_error=1" go test -v -race -count 10 ./...
+        run: make test-race
       - name: golangci-lint
         uses: golangci/golangci-lint-action@v9
       - name: Output coverage

.github/workflows/fuzz.yml

@@ -0,0 +1,30 @@
+name: Fuzz
+
+permissions:
+  contents: read
+
+on:
+  schedule:
+    - cron: '0 6 * * *'   # daily, 06:00 UTC
+  workflow_dispatch:       # manual trigger from Actions tab
+
+jobs:
+  fuzz:
+    name: Fuzz
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v6
+      - name: Install Go
+        uses: actions/setup-go@v6
+        with:
+          go-version: 1.25.x
+      - name: Fuzz
+        run: make fuzz FUZZTIME=5m
+      - name: Upload crash inputs
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: fuzz-crashers
+          path: '**/testdata/fuzz/**'
+          if-no-files-found: ignore

.gitignore

@@ -1,2 +1,3 @@
 /.idea
 /coverage.out
+/coverage.html

Makefile

@@ -0,0 +1,59 @@
+.PHONY: all ci build test test-race lint fuzz bench fix cover help
+
+# Default: the fast loop (build + test + lint). Use during active development.
+all: build test lint
+
+# Everything CI runs. Use before submitting a PR.
+ci: build test-race lint
+
+build:
+	go build -mod=readonly ./...
+
+# Fast unit tests — includes property tests and fuzz seed corpora
+test:
+	go test ./...
+
+# What CI runs: race detector, 10 iterations, halt on first race
+test-race:
+	env "GORACE=halt_on_error=1" go test -race -count 10 ./...
+
+lint:
+	golangci-lint run
+
+# Coverage HTML report (opens in browser on most systems; else see coverage.html)
+cover:
+	go test -covermode=count -coverprofile=coverage.out ./...
+	go tool cover -html=coverage.out -o coverage.html
+	@echo "wrote coverage.html"
+
+# Active fuzzing. One target at a time, FUZZTIME per target (default 30s).
+# Example: make fuzz FUZZTIME=2m
+FUZZTIME ?= 30s
+FUZZ_TARGETS := FuzzRollingCounterOps FuzzRollingCounterJSON \
+	FuzzSortedDurationsPercentile FuzzRollingBucketAdvance FuzzTimedCheckJSON
+fuzz:
+	@for t in $(FUZZ_TARGETS); do \
+		echo "=== fuzz $$t ($(FUZZTIME)) ==="; \
+		go test -fuzz="^$$t$$" -fuzztime=$(FUZZTIME) ./faststats/ || exit 1; \
+	done
+
+bench:
+	go test -benchmem -run=^$$ -bench=. ./...
+
+# Auto-format: gofmt + goimports on all source
+fix:
+	gofmt -s -w .
+	@command -v goimports >/dev/null 2>&1 && goimports -w . || echo "goimports not installed, skipped"
+
+help:
+	@echo "Targets:"
+	@echo "  make             fast dev loop: build + test + lint (~5s)"
+	@echo "  make ci          everything CI runs — use before submitting a PR (~1min)"
+	@echo "  make build       compile all packages"
+	@echo "  make test        unit tests (includes property tests, fuzz seeds)"
+	@echo "  make test-race   race detector, -count 10"
+	@echo "  make lint        golangci-lint run"
+	@echo "  make fuzz        active fuzzing, FUZZTIME per target (default 30s)"
+	@echo "  make bench       all benchmarks"
+	@echo "  make cover       generate coverage.html"
+	@echo "  make fix         gofmt + goimports"

README.md

@@ -451,7 +451,14 @@ BenchmarkCiruits/iand_circuit/Default/passing/75-8       	 5000000	       349 ns
 
 # [Development](https://github.com/cep21/circuit/blob/master/Makefile)
 
-Make sure your tests pass with `go test` and your lints pass with `golangci-lint run`.
+```bash
+make          # fast dev loop: build + test + lint (~5s)
+make ci       # everything CI runs — use before submitting a PR (~1min)
+make fuzz     # active fuzzing (FUZZTIME per target, default 30s)
+make help     # full target list
+```
+
+`make ci` mirrors the GitHub Actions workflow: build, `go test -race -count 10`, and `golangci-lint run`. If it passes locally, CI should pass.
 
 # [Example](https://github.com/cep21/circuit/blob/master/example/main.go)