Add a target to reproduce fuzz testcase

Makefile

@@ -582,3 +582,9 @@ lint-jsonnet:
 fmt-jsonnet:
 	@find . -name 'vendor' -prune -o -name '*.libsonnet' -print -o -name '*.jsonnet' -print | \
 		xargs -n 1 -- jsonnetfmt -i
+
+# usage: FUZZ_TESTCASE_PATH=/tmp/testcase make test-fuzz
+# this will run the fuzzing using /tmp/testcase and save benchmark locally.
+test-fuzz:
+	go test -timeout 30s -tags dev,gofuzz -cpuprofile cpu.prof -memprofile mem.prof  \
+		-run ^Test_Fuzz$$ github.com/grafana/loki/pkg/logql -v -count=1 -timeout=0s

pkg/logql/fuzz_test.go

@@ -0,0 +1,20 @@
+// +build gofuzz
+
+package logql
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+const fuzzTestCaseEnvName = "FUZZ_TESTCASE_PATH"
+
+func Test_Fuzz(t *testing.T) {
+	fuzzTestPath := os.Getenv(fuzzTestCaseEnvName)
+	data, err := ioutil.ReadFile(fuzzTestPath)
+	require.NoError(t, err)
+	_, _ = ParseExpr(string(data))
+}