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_get_bundle_path_plugin/main.go

@@ -0,0 +1,31 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package main
+
+import (
+	"fmt"
+	"path/filepath"
+
+	"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) {
+	bundlePath, err := p.API.GetBundlePath()
+	if err != nil {
+		return nil, err.Error() + "failed get bundle path"
+	} else if bundlePathFromConfig, _ := filepath.Abs(filepath.Join(*p.API.GetConfig().PluginSettings.Directory, "test_get_bundle_path_plugin")); bundlePathFromConfig != bundlePath {
+		return nil, fmt.Sprintf("Invalid bundle path returned: %v vs %v", bundlePathFromConfig, bundlePath)
+	}
+
+	return nil, ""
+}
+
+func main() {
+	plugin.ClientMain(&MyPlugin{})
+}