Made mock-fts take its base URL from --addr when --base-url isn't given

cmd/mock-fts/main_test.go

@@ -0,0 +1,34 @@
+package main
+
+import "testing"
+
+// Without --base-url, the base URL comes from --addr, with localhost for an
+// unspecified host.
+func TestBaseURLFromAddr(t *testing.T) {
+	tests := []struct {
+		addr string
+		want string
+	}{
+		{":8080", "http://localhost:8080"},
+		{"0.0.0.0:8080", "http://localhost:8080"},
+		{"[::]:8080", "http://localhost:8080"},
+		{"127.0.0.1:18080", "http://127.0.0.1:18080"},
+		{"[::1]:8080", "http://[::1]:8080"},
+		{"mock.example.com:80", "http://mock.example.com:80"},
+	}
+	for _, tt := range tests {
+		got, err := baseURLFromAddr(tt.addr)
+		if err != nil || got != tt.want {
+			t.Errorf("baseURLFromAddr(%q) = %q, %v; want %q", tt.addr, got, err, tt.want)
+		}
+	}
+}
+
+// An address without a port, or with port 0, is refused.
+func TestBaseURLFromAddrRefused(t *testing.T) {
+	for _, addr := range []string{"localhost", ":0"} {
+		if got, err := baseURLFromAddr(addr); err == nil {
+			t.Errorf("baseURLFromAddr(%q) = %q; want an error", addr, got)
+		}
+	}
+}