diff --git a/discovery/discovery_test.go b/discovery/discovery_test.go
index 427a7990b..02fc2f981 100644
--- a/discovery/discovery_test.go
+++ b/discovery/discovery_test.go
@@ -18,11 +18,137 @@ import (
 	"sync"
 	"sync/atomic"
 	"testing"
+	"time"
 
 	"github.com/prometheus/prometheus/config"
 	yaml "gopkg.in/yaml.v2"
 )
 
+func TestSingleTargetSetWithSingleProviderOnlySendsNewTargetGroups(t *testing.T) {
+
+	testCases := [][]update{
+		[]update{}, // No updates.
+
+		[]update{{[]string{}, 0}}, // Empty initials.
+
+		[]update{{[]string{}, 6000}}, // Empty initials with a delay.
+
+		[]update{{[]string{"initial1", "initial2"}, 0}}, // Initials only.
+
+		[]update{{[]string{"initial1", "initial2"}, 6000}}, // Initials only but after a delay.
+
+		[]update{ // Initials and new groups.
+			{[]string{"initial1", "initial2"}, 0},
+			{[]string{"update1", "update2"}, 0},
+		},
+
+		[]update{ // Initials and new groups after a delay.
+			{[]string{"initial1", "initial2"}, 6000},
+			{[]string{"update1", "update2"}, 500},
+		},
+
+		[]update{
+			{[]string{"initial1", "initial2"}, 100},
+			{[]string{"update1", "update2", "update3", "update4", "update5", "update6", "update7", "update8", "update9", "update10", "update11"}, 100},
+		},
+
+		[]update{
+			{[]string{"initial1"}, 10},
+			{[]string{"update1"}, 45},
+			{[]string{"update2", "update3", "update4"}, 0},
+			{[]string{"update5"}, 10},
+			{[]string{"update6", "update7", "update8", "update9"}, 70},
+		},
+
+		[]update{
+			{[]string{"initial1", "initial2"}, 5},
+			{[]string{}, 100},
+			{[]string{"update1", "update2"}, 100},
+			{[]string{"update3", "update4", "update5"}, 70},
+		},
+	}
+
+	for i, updates := range testCases {
+
+		expectedGroups := make(map[string]struct{})
+		for _, update := range updates {
+			for _, target := range update.targets {
+				expectedGroups[target] = struct{}{}
+			}
+		}
+
+		var wg sync.WaitGroup
+		wg.Add(1)
+
+		isFirstSyncCall := true
+		var initialGroups []*config.TargetGroup
+		var syncedGroups []*config.TargetGroup
+
+		targetSet := NewTargetSet(&mockSyncer{
+			sync: func(tgs []*config.TargetGroup) {
+				syncedGroups = tgs
+
+				if isFirstSyncCall {
+					isFirstSyncCall = false
+					initialGroups = tgs
+				}
+
+				if len(tgs) == len(expectedGroups) {
+					// All the groups are sent, we can start asserting.
+					wg.Done()
+				}
+			},
+		})
+
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		tp := newMockTargetProvider(updates)
+		targetProviders := map[string]TargetProvider{}
+		targetProviders["testProvider"] = tp
+
+		go targetSet.Run(ctx)
+		targetSet.UpdateProviders(targetProviders)
+
+		finalize := make(chan struct{})
+		go func() {
+			defer close(finalize)
+			wg.Wait()
+		}()
+
+		select {
+		case <-time.After(20000 * time.Millisecond):
+			t.Errorf("In test case %v: Test timed out after 20000 millisecond. All targets should be sent within the timeout", i)
+
+		case <-finalize:
+
+			if *tp.callCount != 1 {
+				t.Errorf("In test case %v: TargetProvider Run should be called once only, was called %v times", i, *tp.callCount)
+			}
+
+			if len(updates) > 0 && updates[0].interval > 5000 {
+				// If the initial set of targets never arrive or arrive after 5 seconds.
+				// The first sync call should receive empty set of targets.
+				if len(initialGroups) != 0 {
+					t.Errorf("In test case %v: Expecting 0 initial target groups, received %v", i, len(initialGroups))
+				}
+			}
+
+			if len(syncedGroups) != len(expectedGroups) {
+				t.Errorf("In test case %v: Expecting %v target groups in total, received %v", i, len(expectedGroups), len(syncedGroups))
+			}
+
+			for _, tg := range syncedGroups {
+				if _, ok := expectedGroups[tg.Source]; ok == false {
+					t.Errorf("In test case %v: '%s' does not exist in expected target groups: %s", i, tg.Source, expectedGroups)
+				} else {
+					delete(expectedGroups, tg.Source) // Remove used targets from the map.
+				}
+			}
+		}
+	}
+}
+
 func TestTargetSetRecreatesTargetGroupsEveryRun(t *testing.T) {
 
 	verifyPresence := func(tgroups map[string]*config.TargetGroup, name string, present bool) {
@@ -76,25 +202,6 @@ static_configs:
 	verifyPresence(ts.tgroups, "static/0/1", false)
 }
 
-type mockSyncer struct {
-	sync func(tgs []*config.TargetGroup)
-}
-
-func (s *mockSyncer) Sync(tgs []*config.TargetGroup) {
-	if s.sync != nil {
-		s.sync(tgs)
-	}
-}
-
-type mockTargetProvider struct {
-	callCount *uint32
-}
-
-func (tp mockTargetProvider) Run(ctx context.Context, up chan<- []*config.TargetGroup) {
-	atomic.AddUint32(tp.callCount, 1)
-	up <- []*config.TargetGroup{{Source: "dummySource"}}
-}
-
 func TestTargetSetRunsSameTargetProviderMultipleTimes(t *testing.T) {
 
 	var wg sync.WaitGroup
@@ -112,10 +219,7 @@ func TestTargetSetRunsSameTargetProviderMultipleTimes(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
-	tp := mockTargetProvider{}
-	var callCount uint32
-	tp.callCount = &callCount
-
+	tp := newMockTargetProvider([]update{{[]string{"initial1", "initial2"}, 10}})
 	targetProviders := map[string]TargetProvider{}
 	targetProviders["testProvider"] = tp
 
@@ -126,7 +230,59 @@ func TestTargetSetRunsSameTargetProviderMultipleTimes(t *testing.T) {
 	ts2.UpdateProviders(targetProviders)
 	wg.Wait()
 
-	if callCount != 2 {
-		t.Errorf("Was expecting 2 calls received %v", callCount)
+	if *tp.callCount != 2 {
+		t.Errorf("Was expecting 2 calls received %v", tp.callCount)
+	}
+}
+
+type mockSyncer struct {
+	sync func(tgs []*config.TargetGroup)
+}
+
+func (s *mockSyncer) Sync(tgs []*config.TargetGroup) {
+	if s.sync != nil {
+		s.sync(tgs)
+	}
+}
+
+type mockTargetProvider struct {
+	callCount *uint32
+	updates   []update
+	up        chan<- []*config.TargetGroup
+}
+
+type update struct {
+	targets  []string
+	interval time.Duration
+}
+
+func newMockTargetProvider(updates []update) mockTargetProvider {
+	var callCount uint32
+
+	tp := mockTargetProvider{
+		callCount: &callCount,
+		updates:   updates,
+	}
+
+	return tp
+}
+
+func (tp mockTargetProvider) Run(ctx context.Context, up chan<- []*config.TargetGroup) {
+	atomic.AddUint32(tp.callCount, 1)
+	tp.up = up
+	tp.sendUpdates()
+}
+
+func (tp mockTargetProvider) sendUpdates() {
+	for _, update := range tp.updates {
+
+		time.Sleep(update.interval * time.Millisecond)
+
+		tgs := make([]*config.TargetGroup, len(update.targets))
+		for i, tg := range update.targets {
+			tgs[i] = &config.TargetGroup{Source: tg}
+		}
+
+		tp.up <- tgs
 	}
 }