[linux] Fix #900, skip or fix failing tests in docker

TestGetProcInodesAll: create a server so there are some opened inodes
TestUsers: skip if Users is empty, because of an empty /var/run/utmp
Test_Process_Groups: skip if Groups is empty
TestConnectionsMax: skip on CI, not only CircleCI

host/host_test.go

@@ -67,7 +67,7 @@ func TestUsers(t *testing.T) {
 	}
 	empty := UserStat{}
 	if len(v) == 0 {
-		t.Fatal("Users is empty")
+		t.Skip("Users is empty")
 	}
 	for _, u := range v {
 		if u == empty {

net/net_linux_test.go

@@ -3,6 +3,7 @@ package net
 import (
 	"fmt"
 	"io/ioutil"
+	"net"
 	"os"
 	"strings"
 	"syscall"
@@ -77,9 +78,27 @@ func TestIOCountersByFileParsing(t *testing.T) {
 }
 
 func TestGetProcInodesAll(t *testing.T) {
-	if os.Getenv("CIRCLECI") == "true" {
-		t.Skip("Skip CI")
+	waitForServer := make(chan bool)
+	go func() { // TCP listening goroutine to have some opened inodes even in CI
+		addr, err := net.ResolveTCPAddr("tcp", "localhost:0") // dynamically get a random open port from OS
+		if err != nil {
+			t.Skip("unable to resolve localhost:", err)
+		}
+		l, err := net.ListenTCP(addr.Network(), addr)
+		if err != nil {
+			t.Skip(fmt.Sprintf("unable to listen on %v: %v", addr, err))
+		}
+		defer l.Close()
+		waitForServer <- true
+		for {
+			conn, err := l.Accept()
+			if err != nil {
+				t.Skip("unable to accept connection:", err)
+			}
+			defer conn.Close()
 		}
+	}()
+	<-waitForServer
 
 	root := common.HostProc("")
 	v, err := getProcInodesAll(root, 0)
@@ -88,7 +107,7 @@ func TestGetProcInodesAll(t *testing.T) {
 }
 
 func TestConnectionsMax(t *testing.T) {
-	if os.Getenv("CIRCLECI") == "true" {
+	if os.Getenv("CI") != "" {
 		t.Skip("Skip CI")
 	}
 

process/process_test.go

@@ -253,7 +253,10 @@ func Test_Process_Groups(t *testing.T) {
 	if err != nil {
 		t.Errorf("getting groups error %v", err)
 	}
-	if len(v) <= 0 || v[0] < 0 {
+	if len(v) == 0 {
+		t.Skip("Groups is empty")
+	}
+	if v[0] < 0 {
 		t.Errorf("invalid Groups: %v", v)
 	}
 }