diff --git a/irc_channel.go b/irc_channel.go
new file mode 100644
index 0000000..3bca3be
--- /dev/null
+++ b/irc_channel.go
@@ -0,0 +1,39 @@
+package main
+
+// Channel represents an IRC channel. It maps to Slack's groups and channels.
+// Private messages are handled differently.
+type Channel struct {
+	Members []string
+	Topic   string
+	// Slack groups are different from channels. Here I try to uniform them for
+	// IRC, but I still need to know which is which to use the right API calls.
+	IsGroup bool
+}
+
+// MembersDiff compares the members of this channel with another members list
+// and return a slice of members who joined and a slice of members who left.
+func (c Channel) MembersDiff(otherMembers []string) ([]string, []string) {
+	var membersMap = map[string]bool{}
+	for _, m := range c.Members {
+		membersMap[m] = true
+	}
+	var otherMembersMap = map[string]bool{}
+	for _, m := range otherMembers {
+		otherMembersMap[m] = true
+	}
+
+	added := make([]string, 0)
+	for _, m := range otherMembers {
+		if _, ok := membersMap[m]; !ok {
+			added = append(added, m)
+		}
+	}
+
+	removed := make([]string, 0)
+	for _, m := range c.Members {
+		if _, ok := otherMembersMap[m]; !ok {
+			removed = append(removed, m)
+		}
+	}
+	return added, removed
+}
diff --git a/irc_channel_test.go b/irc_channel_test.go
new file mode 100644
index 0000000..67b3145
--- /dev/null
+++ b/irc_channel_test.go
@@ -0,0 +1,27 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestMembersDiffEmpty(t *testing.T) {
+	c := Channel{Members: []string{}}
+	a, r := c.MembersDiff([]string{})
+	if len(a) != 0 {
+		t.Fatalf("Added members: %v; want empty list", a)
+	}
+	if len(r) != 0 {
+		t.Fatalf("Removed members: %v; want empty list", r)
+	}
+}
+
+func TestMembersDiffNonEmpty(t *testing.T) {
+	c := Channel{Members: []string{"removed1"}}
+	a, r := c.MembersDiff([]string{"added1"})
+	if !(len(a) == 1 && a[0] == "added1") {
+		t.Fatalf("Added members: %v; want: %v", a, []string{"added1"})
+	}
+	if !(len(r) == 1 && r[0] == "removed1") {
+		t.Fatalf("Removed members: %v; want: %v", a, []string{"removed1"})
+	}
+}
diff --git a/irc_context.go b/irc_context.go
index 6b0d740..f09d40a 100644
--- a/irc_context.go
+++ b/irc_context.go
@@ -8,44 +8,6 @@ import (
 	"github.com/nlopes/slack"
 )
 
-// Channel represents an IRC channel. It maps to Slack's groups and channels.
-// Private messages are handled differently.
-type Channel struct {
-	Members []string
-	Topic   string
-	// Slack groups are different from channels. Here I try to uniform them for
-	// IRC, but I still need to know which is which to use the right API calls.
-	IsGroup bool
-}
-
-// MembersDiff compares the members of this channel with another members list
-// and return a slice of members who joined and a slice of members who left.
-func (c Channel) MembersDiff(otherMembers []string) ([]string, []string) {
-	var membersMap = map[string]bool{}
-	for _, m := range c.Members {
-		membersMap[m] = true
-	}
-	var otherMembersMap = map[string]bool{}
-	for _, m := range otherMembers {
-		otherMembersMap[m] = true
-	}
-
-	added := make([]string, 0)
-	for _, m := range otherMembers {
-		if _, ok := membersMap[m]; !ok {
-			added = append(added, m)
-		}
-	}
-
-	removed := make([]string, 0)
-	for _, m := range c.Members {
-		if _, ok := otherMembersMap[m]; !ok {
-			removed = append(removed, m)
-		}
-	}
-	return added, removed
-}
-
 // IrcContext holds the client context information
 type IrcContext struct {
 	Conn           *net.TCPConn