create helper to validate channel name

add test cases

subscription/subscription_test.go

@@ -0,0 +1,73 @@
+package subscription
+
+import "testing"
+
+/*
+ assertEqual( ["/**", "/foo", "/*"],
+                   Channel.expand("/foo") )
+
+      assertEqual( ["/**", "/foo/bar", "/foo/*", "/foo/**"],
+                   Channel.expand("/foo/bar") )
+
+      assertEqual( ["/**", "/foo/bar/qux", "/foo/bar/*", "/foo/**", "/foo/bar/**"],
+*/
+func TestIsValidChannel(t *testing.T) {
+	type args struct {
+		channel string
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			name: "single asterisc",
+			args: args{
+				channel: "/*",
+			},
+			want: true,
+		},
+		{
+			name: "double asterisc",
+			args: args{
+				channel: "/**",
+			},
+			want: true,
+		},
+		{
+			name: "regular channel",
+			args: args{
+				channel: "/foo",
+			},
+			want: true,
+		},
+		{
+			name: "regular channel 2",
+			args: args{
+				channel: "/foo/bar",
+			},
+			want: true,
+		},
+		{
+			name: "invalid slash ending",
+			args: args{
+				channel: "/foo/",
+			},
+			want: false,
+		},
+		{
+			name: "invalid asterisc at the middle",
+			args: args{
+				channel: "/foo/**/bar",
+			},
+			want: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := IsValidChannel(tt.args.channel); got != tt.want {
+				t.Errorf("IsValidChannel() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}