Add processes exporter (#950)

* Add processes exporter

Signed-off-by: Pavel Kutishchev <pavel.kutishchev@olx.com>
Signed-off-by: Ben Kochie <superq@gmail.com>

collector/processes_linux_test.go

@@ -0,0 +1,47 @@
+// Copyright 2018 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !noprocesses
+
+package collector
+
+import (
+	"testing"
+
+	"gopkg.in/alecthomas/kingpin.v2"
+)
+
+func TestReadProcessStatus(t *testing.T) {
+	if _, err := kingpin.CommandLine.Parse([]string{"--path.procfs", "fixtures/proc"}); err != nil {
+		t.Fatal(err)
+	}
+	want := 1
+	pids, states, threads, err := getAllocatedThreads()
+	if err != nil {
+		t.Fatalf("Cannot retrieve data from procfs getAllocatedThreads function: %v ", err)
+	}
+	if threads < want {
+		t.Fatalf("Current threads: %d Shouldn't be less than wanted %d", threads, want)
+	}
+	if states == nil {
+
+		t.Fatalf("Process states cannot be nil %v:", states)
+	}
+	maxPid, err := readUintFromFile(procFilePath("sys/kernel/pid_max"))
+	if err != nil {
+		t.Fatalf("Unable to retrieve limit number of maximum pids alloved %v\n", err)
+	}
+	if uint64(pids) > maxPid || pids == 0 {
+		t.Fatalf("Total running pids cannot be greater than %d or equals to 0", maxPid)
+	}
+}