[PLT-5170] Add join the channel system message for the person who created the channel (#7299)

* add join the channel system message for the person who created the channel

* update test

5 files changed, 46 insertions, 12 deletions

diff --git a/api/admin_test.go b/api/admin_test.go
index bfc678adc..07504c4d1 100644
--- a/api/admin_test.go
+++ b/api/admin_test.go
@@ -246,7 +246,7 @@ func TestGetTeamAnalyticsStandard(t *testing.T) {
 			t.Fatal()
 		}
 
-		if rows[2].Value != 6 {
+		if rows[2].Value != 9 {
 			t.Log(rows.ToJson())
 			t.Fatal()
 		}
diff --git a/api/command_test.go b/api/command_test.go
index bc8aca6aa..0d575d702 100644
--- a/api/command_test.go
+++ b/api/command_test.go
@@ -4,6 +4,7 @@
 package api
 
 import (
+	"strings"
 	"testing"
 	"time"
 
@@ -256,9 +257,22 @@ func TestTestCommand(t *testing.T) {
 
 	time.Sleep(100 * time.Millisecond)
 
-	p1 := Client.Must(Client.GetPosts(channel1.Id, 0, 2, "")).Data.(*model.PostList)
-	if len(p1.Order) != 1 {
-		t.Fatal("Test command failed to send")
+	p1 := Client.Must(Client.GetPosts(channel1.Id, 0, 10, "")).Data.(*model.PostList)
+	// including system 'joined' message
+	if len(p1.Order) != 2 {
+		t.Fatal("Test command response failed to send")
+	}
+
+	cmdPosted := false
+	for _, post := range p1.Posts {
+		if strings.Contains(post.Message, "test command response") {
+			cmdPosted = true
+			break
+		}
+	}
+
+	if !cmdPosted {
+		t.Fatal("Test command response failed to post")
 	}
 
 	cmd2 := &model.Command{
@@ -276,8 +290,8 @@ func TestTestCommand(t *testing.T) {
 
 	time.Sleep(100 * time.Millisecond)
 
-	p2 := Client.Must(Client.GetPosts(channel1.Id, 0, 2, "")).Data.(*model.PostList)
-	if len(p2.Order) != 2 {
+	p2 := Client.Must(Client.GetPosts(channel1.Id, 0, 10, "")).Data.(*model.PostList)
+	if len(p2.Order) != 3 {
 		t.Fatal("Test command failed to send")
 	}
 }
diff --git a/api/post_test.go b/api/post_test.go
index 29c1f791a..c31439c82 100644
--- a/api/post_test.go
+++ b/api/post_test.go
@@ -613,8 +613,8 @@ func TestGetPostsBeforeAfter(t *testing.T) {
 		t.Fatal("wrong order")
 	}
 
-	if len(r1.Posts) != 3 {
-		t.Log(r1.Posts)
+	// including created post from test helper and system 'joined' message
+	if len(r1.Posts) != 4 {
 		t.Fatal("wrong size")
 	}
 
@@ -927,8 +927,8 @@ func TestDeletePosts(t *testing.T) {
 
 	r2 := Client.Must(Client.GetPosts(channel1.Id, 0, 10, "")).Data.(*model.PostList)
 
-	if len(r2.Posts) != 5 {
-		t.Fatal("should have returned 5 items")
+	if post := r2.Posts[post3.Id]; post != nil {
+		t.Fatal("should have not returned deleted post")
 	}
 
 	time.Sleep(10 * time.Millisecond)
diff --git a/api4/command_test.go b/api4/command_test.go
index 8f0303c55..3c61f82b1 100644
--- a/api4/command_test.go
+++ b/api4/command_test.go
@@ -4,6 +4,7 @@
 package api4
 
 import (
+	"strings"
 	"testing"
 
 	"github.com/mattermost/platform/app"
@@ -416,10 +417,22 @@ func TestExecuteCommand(t *testing.T) {
 	}
 
 	posts, err := app.GetPostsPage(channel.Id, 0, 10)
-	if err != nil || posts == nil || len(posts.Order) != 2 {
+	if err != nil || posts == nil || len(posts.Order) != 3 {
 		t.Fatal("Test command failed to send")
 	}
 
+	cmdPosted := false
+	for _, post := range posts.Posts {
+		if strings.Contains(post.Message, "test command response") {
+			cmdPosted = true
+			break
+		}
+	}
+
+	if !cmdPosted {
+		t.Fatal("Test command response failed to post")
+	}
+
 	getCmd := &model.Command{
 		CreatorId: th.BasicUser.Id,
 		TeamId:    th.BasicTeam.Id,
@@ -440,7 +453,7 @@ func TestExecuteCommand(t *testing.T) {
 	}
 
 	posts, err = app.GetPostsPage(channel.Id, 0, 10)
-	if err != nil || posts == nil || len(posts.Order) != 3 {
+	if err != nil || posts == nil || len(posts.Order) != 4 {
 		t.Fatal("Test command failed to send")
 	}
 
diff --git a/app/channel.go b/app/channel.go
index 417659c49..a0684ddc8 100644
--- a/app/channel.go
+++ b/app/channel.go
@@ -126,6 +126,13 @@ func CreateChannelWithUser(channel *model.Channel, userId string) (*model.Channe
 		return nil, err
 	}
 
+	var user *model.User
+	if user, err = GetUser(userId); err != nil {
+		return nil, err
+	}
+
+	postJoinChannelMessage(user, channel)
+
 	message := model.NewWebSocketEvent(model.WEBSOCKET_EVENT_CHANNEL_CREATED, "", "", userId, nil)
 	message.Add("channel_id", channel.Id)
 	message.Add("team_id", channel.TeamId)