diff --git a/test/utils/command_line_stream.cpp b/test/utils/command_line_stream.cpp
new file mode 100644
index 00000000..8c1639e3
--- /dev/null
+++ b/test/utils/command_line_stream.cpp
@@ -0,0 +1,69 @@
+#if __has_include(<catch2/catch_test_macros.hpp>)
+#include <catch2/catch_test_macros.hpp>
+#else
+#include <catch2/catch.hpp>
+#endif
+
+#include <glibmm/main.h>
+
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "util/command_line_stream.hpp"
+
+namespace {
+
+struct StreamResult {
+  std::vector<std::string> lines;
+  std::optional<int> exit_code;
+  bool timed_out = false;
+};
+
+auto run_stream_command(const std::string& cmd) -> StreamResult {
+  StreamResult result;
+  auto loop = Glib::MainLoop::create();
+
+  auto timeout = Glib::signal_timeout().connect(
+      [&]() {
+        result.timed_out = true;
+        loop->quit();
+        return false;
+      },
+      3000);
+
+  waybar::util::command::LineStream stream(
+      "",
+      [&](const std::string& line) { result.lines.push_back(line); },
+      [&](int exit_code) {
+        result.exit_code = exit_code;
+        loop->quit();
+      });
+
+  stream.start(cmd);
+  loop->run();
+  timeout.disconnect();
+  return result;
+}
+
+}  // namespace
+
+TEST_CASE("command::LineStream emits complete lines and flushes trailing output",
+          "[util][command_line_stream]") {
+  const auto result = run_stream_command("printf 'first\\nsecond'");
+
+  REQUIRE_FALSE(result.timed_out);
+  REQUIRE(result.exit_code.has_value());
+  REQUIRE(*result.exit_code == 0);
+  REQUIRE(result.lines == std::vector<std::string>{"first", "second"});
+}
+
+TEST_CASE("command::LineStream does not emit an extra line after newline-terminated output",
+          "[util][command_line_stream]") {
+  const auto result = run_stream_command("printf 'first\\nsecond\\n'");
+
+  REQUIRE_FALSE(result.timed_out);
+  REQUIRE(result.exit_code.has_value());
+  REQUIRE(*result.exit_code == 0);
+  REQUIRE(result.lines == std::vector<std::string>{"first", "second"});
+}
diff --git a/test/utils/fixtures/GlibTestsFixture.hpp b/test/utils/fixtures/GlibTestsFixture.hpp
index a21c8e07..95ce7f95 100644
--- a/test/utils/fixtures/GlibTestsFixture.hpp
+++ b/test/utils/fixtures/GlibTestsFixture.hpp
@@ -6,10 +6,16 @@
 class GlibTestsFixture : public sigc::trackable {
  public:
   GlibTestsFixture() : main_loop_{Glib::MainLoop::create()} {}
+  ~GlibTestsFixture() { timeout_.disconnect(); }
 
   void setTimeout(int timeout) {
-    Glib::signal_timeout().connect_once([]() { throw std::runtime_error("Test timed out"); },
-                                        timeout);
+    timeout_.disconnect();
+    timeout_ = Glib::signal_timeout().connect(
+        []() {
+          throw std::runtime_error("Test timed out");
+          return false;
+        },
+        timeout);
   }
 
   void run(std::function<void()> fn) {
@@ -21,4 +27,5 @@ class GlibTestsFixture : public sigc::trackable {
 
  protected:
   Glib::RefPtr<Glib::MainLoop> main_loop_;
+  sigc::connection timeout_;
 };
diff --git a/test/utils/meson.build b/test/utils/meson.build
index e8dd37fa..0d9130de 100644
--- a/test/utils/meson.build
+++ b/test/utils/meson.build
@@ -15,8 +15,10 @@ test_src = files(
     'SafeSignal.cpp',
     'sleeper_thread.cpp',
     'command.cpp',
+    'command_line_stream.cpp',
     'css_reload_helper.cpp',
     '../../src/util/css_reload_helper.cpp',
+    '../../src/util/command_line_stream.cpp',
 )
 
 if tz_dep.found()