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_search_teams_plugin/main.go

@@ -0,0 +1,56 @@
+// 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) {
+
+	teams, err := p.API.SearchTeams("{{.BasicTeam.Name}}")
+	if err != nil {
+		return nil, "search failed: " + err.Message
+	}
+	if len(teams) != 1 {
+		return nil, fmt.Sprintf("search failed, wrong number of teams: %v", len(teams))
+	}
+
+	teams, err = p.API.SearchTeams("{{.BasicTeam.DisplayName}}")
+	if err != nil {
+		return nil, "search failed: " + err.Message
+	}
+	if len(teams) != 1 {
+		return nil, fmt.Sprintf("search failed, wrong number of teams: %v", len(teams))
+	}
+
+	teams, err = p.API.SearchTeams("{{.BasicTeam.Name}}"[:3])
+
+	if err != nil {
+		return nil, "search failed: " + err.Message
+	}
+	if len(teams) != 1 {
+		return nil, fmt.Sprintf("search failed, wrong number of teams: %v", len(teams))
+	}
+
+	teams, err = p.API.SearchTeams("not found")
+	if err != nil {
+		return nil, "search failed: " + err.Message
+	}
+	if len(teams) != 0 {
+		return nil, fmt.Sprintf("search failed, wrong number of teams: %v", len(teams))
+	}
+	return nil, ""
+}
+
+func main() {
+	plugin.ClientMain(&MyPlugin{})
+}