MM-14559 Rewrite existing plugin API tests to exclusively test via actual plugin (#10494)

* initial work on rewriting test cases using the raw literal format

* split out the embedded tests into separate file and implement the test using a generic tester function

* initial work on rewriting test cases using the raw literal format

* split out the embedded tests into separate file and implement the test using a generic tester function

* moved tests to separate dir to avoid conflicts

* removed duplicate files

* added license header

* fixed plugin paths

* moved all trivial tests to separate files
created "meta-test" that scans a folder of api tests and runs them

* remove rpc tests from make

* use fileutil.FindDir instead of pwd
clean up the test files

tests/plugin_tests/test_update_user_status_plugin/main.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package main
+
+import (
+	"fmt"
+
+	"github.com/mattermost/mattermost-server/model"
+	"github.com/mattermost/mattermost-server/plugin"
+)
+
+type MyPlugin struct {
+	plugin.MattermostPlugin
+}
+
+func (p *MyPlugin) MessageWillBePosted(c *plugin.Context, post *model.Post) (*model.Post, string) {
+	uid := "{{.BasicUser.Id}}"
+
+	statuses := []string{model.STATUS_ONLINE, model.STATUS_AWAY, model.STATUS_DND, model.STATUS_OFFLINE}
+
+	for _, s := range statuses {
+		status, err := p.API.UpdateUserStatus(uid, s)
+		if err != nil {
+			return nil, err.Error()
+		}
+		if status == nil {
+			return nil, "Status was expected, got nil"
+		}
+		if s != status.Status {
+			return nil, fmt.Sprintf("Invalid status returned: %v != %v", s, status.Status)
+		}
+
+	}
+
+	status, err := p.API.UpdateUserStatus(uid, "notrealstatus")
+	if err == nil {
+		return nil, "Expected to get an error while updating invalid user status"
+	}
+	if status != nil {
+		return nil, "Status was expected to be nil, got: " + status.Status
+	}
+
+	return nil, ""
+}
+
+func main() {
+	plugin.ClientMain(&MyPlugin{})
+}