Add unit tests for printer driver, usb device and usb device factory

tests/printer_service_test/printer_service_test.cpp

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+/*
+    ptrnt - print labels on linux
+    Copyright (C) 2025  Moritz Martinius
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+ */
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include <memory>
+#include <vector>
+
+#include "../../tests/mocks/MockPrinterDriver.hpp"
+#include "../../tests/mocks/MockUsbDevice.hpp"
+#include "core/PrinterDriverFactory.hpp"
+#include "core/PrinterService.hpp"
+
+using ::testing::_;
+using ::testing::NiceMock;
+using ::testing::Return;
+
+namespace ptprnt::core {
+
+// Test fixture for PrinterService tests
+class PrinterServiceTest : public ::testing::Test {
+   protected:
+    void SetUp() override {
+        // Service under test
+        service = std::make_unique<PrinterService>();
+    }
+
+    void TearDown() override { service.reset(); }
+
+    std::unique_ptr<PrinterService> service;
+};
+
+// Test: PrinterService initialization
+TEST_F(PrinterServiceTest, InitializeSuccess) {
+    // PrinterService::initialize() calls UsbDeviceFactory::init()
+    // This will attempt to initialize libusb - we can't easily mock this
+    // without dependency injection, but we can test the call succeeds
+    // when libusb is available
+    EXPECT_TRUE(service->initialize());
+}
+
+// Test: Detect printers when none are connected
+TEST_F(PrinterServiceTest, DetectPrintersNoneFound) {
+    service->initialize();
+
+    auto printers = service->detectPrinters();
+
+    // With no compatible USB devices, we should get an empty list
+    // (This depends on actual USB devices present, so it might find real hardware)
+    // In a real test environment without hardware, this should be empty
+    EXPECT_GE(printers.size(), 0);  // Non-negative count
+}
+
+// Test: Select printer with auto-detect
+TEST_F(PrinterServiceTest, SelectPrinterAuto) {
+    service->initialize();
+    service->detectPrinters();
+
+    auto printer = service->selectPrinter("auto");
+
+    // This will be nullptr if no printers detected
+    // In test environment without hardware, expect nullptr
+    // (Test passes either way - just exercises the code path)
+    if (printer != nullptr) {
+        EXPECT_NE(printer, nullptr);
+        EXPECT_EQ(service->getCurrentPrinter(), printer);
+    } else {
+        EXPECT_EQ(printer, nullptr);
+    }
+}
+
+// Test: Select non-existent printer
+TEST_F(PrinterServiceTest, SelectPrinterNotFound) {
+    service->initialize();
+    service->detectPrinters();
+
+    auto printer = service->selectPrinter("NonExistentPrinter");
+
+    EXPECT_EQ(printer, nullptr);
+    EXPECT_EQ(service->getCurrentPrinter(), nullptr);
+}
+
+// Test: Get current printer when none selected
+TEST_F(PrinterServiceTest, GetCurrentPrinterNoneSelected) {
+    EXPECT_EQ(service->getCurrentPrinter(), nullptr);
+}
+
+// Test: Print label without selecting printer
+TEST_F(PrinterServiceTest, PrintLabelNoPrinterSelected) {
+    // Create a simple label (we need a valid ILabel pointer)
+    std::unique_ptr<graphics::ILabel> label = nullptr;  // nullptr label for this test
+
+    bool result = service->printLabel(std::move(label));
+
+    // Should fail because no printer is selected
+    EXPECT_FALSE(result);
+}
+
+}  // namespace ptprnt::core