Sync channel topics between Slack bridges (#585)

Added logic to allow for configurable synchronisation of topics and purposes of channels between Slack bridges.

bridge/slack/helpers_test.go

@@ -0,0 +1,36 @@
+package bslack
+
+import (
+	"io/ioutil"
+	"testing"
+
+	"github.com/42wim/matterbridge/bridge"
+	"github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestExtractTopicOrPurpose(t *testing.T) {
+	testcases := map[string]struct {
+		input          string
+		wantChangeType string
+		wantOutput     string
+	}{
+		"success - topic type":   {"@someone set channel topic: foo bar", "topic", "foo bar"},
+		"success - purpose type": {"@someone set channel purpose: foo bar", "purpose", "foo bar"},
+		"success - one line":     {"@someone set channel topic: foo bar", "topic", "foo bar"},
+		"success - multi-line":   {"@someone set channel topic: foo\nbar", "topic", "foo\nbar"},
+		"success - cleared":      {"@someone cleared channel topic", "topic", ""},
+		"error - unhandled":      {"some unmatched message", "unknown", ""},
+	}
+
+	logger := logrus.New()
+	logger.SetOutput(ioutil.Discard)
+	cfg := &bridge.Config{Log: logger.WithFields(nil)}
+	b := newBridge(cfg)
+	for name, tc := range testcases {
+		gotChangeType, gotOutput := b.extractTopicOrPurpose(tc.input)
+
+		assert.Equalf(t, tc.wantChangeType, gotChangeType, "This testcase failed: %s", name)
+		assert.Equalf(t, tc.wantOutput, gotOutput, "This testcase failed: %s", name)
+	}
+}