diff --git a/core/dbc_statement_handler.cpp b/core/dbc_statement_handler.cpp
index d4a4ab5..8a44792 100644
--- a/core/dbc_statement_handler.cpp
+++ b/core/dbc_statement_handler.cpp
@@ -368,8 +368,7 @@ void DbcSignalHandler::Handle(const std::string &line, DbcParseContext &context)
 }
 
 void DbcCommentHandler::Handle(const std::string &line, DbcParseContext &context) const {
-    if (line.compare(0U, 4U, "CM_ ") == 0)
-        ParseCommentLine(line, context.database);
+    ParseCommentLine(line, context.database);
 }
 
 DbcStatementDispatcher::DbcStatementDispatcher() {
diff --git a/tests/dbc_coverage_test.cpp b/tests/dbc_coverage_test.cpp
new file mode 100644
index 0000000..2dcb689
--- /dev/null
+++ b/tests/dbc_coverage_test.cpp
@@ -0,0 +1,544 @@
+// Additional regression coverage. Kept separate for review before the first run.
+#include "dbc_parser.h"
+#include "dbc_decode_builder.h"
+#include "dbc_decoder.h"
+#include "dbc_tree_builder.h"
+#include "typefactory.h"
+#include <QtTest>
+#include <QTemporaryFile>
+#include <array>
+#include <limits>
+#include <stdexcept>
+
+namespace {
+DbcDatabase ParseText(const std::string &text) {
+    QTemporaryFile file;
+    if (!file.open()) throw std::runtime_error("Cannot create DBC fixture");
+    if (file.write(text.data(), static_cast<qint64>(text.size())) != static_cast<qint64>(text.size()) || !file.flush())
+        throw std::runtime_error("Cannot write DBC fixture");
+    return DbcParser().ParseFile(file.fileName().toStdString());
+}
+
+DecodeDatabase SingleSignal(const DecodeSignal &signal) {
+    DecodeDatabase database;
+    DecodeFrame frame;
+    frame.canId = 17U;
+    frame.signals.push_back(signal);
+    database.frames.push_back(frame);
+    database.frameIndexByKey.emplace(FrameKey(17U, false), 0U);
+    return database;
+}
+
+// Independent reference: collect the visited bits first, then weight them.
+// Motorola uses a linear MSB-first coordinate instead of sawtooth traversal.
+std::uint64_t ReferenceExtract(const std::vector<std::uint8_t> &data,
+                               ByteOrder order, unsigned start, unsigned length) {
+    std::uint64_t expected = 0;
+    for (unsigned i = 0; i < length; ++i) {
+        const unsigned coordinate = order == ByteOrder::Intel
+            ? start + i : (start / 8U) * 8U + (7U - start % 8U) + i;
+        const unsigned bit = order == ByteOrder::Intel ? coordinate % 8U : 7U - coordinate % 8U;
+        const unsigned weight = order == ByteOrder::Intel ? i : length - 1U - i;
+        expected |= std::uint64_t((data.at(coordinate / 8U) >> bit) & 1U) << weight;
+    }
+    return expected;
+}
+
+struct FactoryBase {
+    virtual ~FactoryBase() = default;
+    virtual int Value() const = 0;
+};
+struct FactoryFirst : FactoryBase {
+    explicit FactoryFirst(std::unique_ptr<int> value) : value(std::move(value)) {}
+    int Value() const override { return *value; }
+    std::unique_ptr<int> value;
+};
+struct FactorySecond : FactoryFirst {
+    using FactoryFirst::FactoryFirst;
+    int Value() const override { return *value + 1; }
+};
+}
+
+class CoverageTest : public QObject {
+    Q_OBJECT
+private Q_SLOTS:
+    void frameLookup();
+    void signedBoundaries_data();
+    void signedBoundaries();
+    void extraction_data();
+    void extraction();
+    void invalidSignalStatus_data();
+    void invalidSignalStatus();
+    void malformedRuntimeMultiplexing_data();
+    void malformedRuntimeMultiplexing();
+    void pgn_data();
+    void pgn();
+    void comments_data();
+    void comments();
+    void fileFormatting_data();
+    void fileFormatting();
+    void missingFile();
+    void builders();
+    void physicalConversion_data();
+    void physicalConversion();
+    void multiplexingScenarios();
+    void multiplexingErrorLocations_data();
+    void multiplexingErrorLocations();
+    void escapedValueDescriptions();
+    void factory();
+};
+
+void CoverageTest::frameLookup() {
+    DbcDecoder decoder;
+    RawCanFrame raw;
+    raw.canId = 17U;
+    DecodeDatabase empty;
+    QVERIFY(decoder.FindFrame(empty, 17U, false) == nullptr);
+    const auto absent = decoder.Decode(empty, raw);
+    QVERIFY(!absent.valid);
+    QVERIFY(absent.definition == nullptr);
+    QVERIFY(absent.signals.empty());
+    DecodeSignal signal;
+    auto database = SingleSignal(signal);
+    QVERIFY(decoder.FindFrame(database, 18U, false) == nullptr);
+    QVERIFY(decoder.FindFrame(database, 17U, true) == nullptr);
+    raw.isExtended = true;
+    QVERIFY(!decoder.Decode(database, raw).valid);
+    raw.isExtended = false;
+    raw.canId = 18U;
+    QVERIFY(!decoder.Decode(database, raw).valid);
+    raw.canId = 17U;
+    database.frameIndexByKey.at(FrameKey(17U, false)) = database.frames.size();
+    QVERIFY(decoder.FindFrame(database, 17U, false) == nullptr);
+    QVERIFY(!decoder.Decode(database, raw).valid);
+    database.frameIndexByKey.at(FrameKey(17U, false)) = 0U;
+    database.frames[0].signals.clear();
+    const auto matched = decoder.Decode(database, raw);
+    QVERIFY(matched.valid);
+    QCOMPARE(matched.definition, &database.frames[0]);
+    QVERIFY(matched.signals.empty());
+}
+
+void CoverageTest::signedBoundaries_data() {
+    QTest::addColumn<int>("order");
+    QTest::addColumn<unsigned>("length");
+    QTest::addColumn<qlonglong>("expected");
+    for (int order = 0; order < 2; ++order) {
+        for (unsigned length : {1U, 2U, 7U, 8U, 31U, 32U, 63U}) {
+            const std::int64_t half = std::int64_t(1) << (length - 1U);
+            const std::array<std::int64_t, 4> values{{0, -1, -half, half - 1}};
+            for (unsigned index = 0; index < values.size(); ++index) {
+                const auto name = QByteArray::number(order) + "-" + QByteArray::number(length) + "-" + QByteArray::number(index);
+                QTest::newRow(name.constData()) << order << length << qlonglong(values[index]);
+            }
+        }
+    }
+}
+
+void CoverageTest::signedBoundaries() {
+    QFETCH(int, order);
+    QFETCH(unsigned, length);
+    QFETCH(qlonglong, expected);
+    DecodeSignal signal;
+    signal.byteOrder = order == 0 ? ByteOrder::Intel : ByteOrder::Motorola;
+    signal.startBit = order == 0 ? 0U : 7U;
+    signal.length = length;
+    signal.valueType = ValueType::Signed;
+    RawCanFrame raw;
+    raw.canId = 17U;
+    raw.data.assign(8U, 0U);
+    const std::uint64_t bits = static_cast<std::uint64_t>(expected);
+    for (unsigned i = 0; i < length; ++i) {
+        const unsigned weight = order == 0 ? i : length - 1U - i;
+        const unsigned position = order == 0 ? i % 8U : 7U - i % 8U;
+        raw.data[i / 8U] |= static_cast<std::uint8_t>(((bits >> weight) & 1U) << position);
+    }
+    const auto database = SingleSignal(signal);
+    const auto result = DbcDecoder().Decode(database, raw);
+    QVERIFY(result.signals[0].valid);
+    QVERIFY(std::holds_alternative<std::int64_t>(result.signals[0].rawValue));
+    QCOMPARE(std::get<std::int64_t>(result.signals[0].rawValue), static_cast<std::int64_t>(expected));
+}
+
+void CoverageTest::extraction_data() {
+    QTest::addColumn<int>("order");
+    QTest::addColumn<unsigned>("start");
+    QTest::addColumn<unsigned>("length");
+    for (int order = 0; order < 2; ++order)
+        for (unsigned start = 0; start < 16U; ++start)
+            for (unsigned length = 1; length <= 64U; ++length) {
+                const auto name = QByteArray::number(order) + "-" + QByteArray::number(start) + "-" + QByteArray::number(length);
+                QTest::newRow(name.constData()) << order << start << length;
+            }
+}
+
+void CoverageTest::extraction() {
+    QFETCH(int, order);
+    QFETCH(unsigned, start);
+    QFETCH(unsigned, length);
+    DecodeSignal signal;
+    signal.byteOrder = order == 0 ? ByteOrder::Intel : ByteOrder::Motorola;
+    signal.startBit = start;
+    signal.length = length;
+    const auto database = SingleSignal(signal);
+    RawCanFrame raw;
+    raw.canId = 17U;
+    const std::vector<std::vector<std::uint8_t>> patterns = {
+        std::vector<std::uint8_t>(10U, 0U), std::vector<std::uint8_t>(10U, 255U),
+        {0xA5, 0x3C, 0x81, 0x7E, 0x12, 0xD4, 0x69, 0xB0, 0x5A, 0xC3}};
+    for (const auto &data : patterns) {
+        raw.data = data;
+        const unsigned firstCoordinate = order == 0 ? start : (start / 8U) * 8U + 7U - start % 8U;
+        raw.data.resize((firstCoordinate + length + 7U) / 8U);
+        const auto decoded = DbcDecoder().Decode(database, raw);
+        QVERIFY(decoded.signals[0].valid);
+        QCOMPARE(std::get<std::uint64_t>(decoded.signals[0].rawValue), ReferenceExtract(data, signal.byteOrder, start, length));
+    }
+}
+
+void CoverageTest::invalidSignalStatus_data() {
+    QTest::addColumn<int>("order");
+    QTest::addColumn<unsigned>("start");
+    QTest::addColumn<unsigned>("length");
+    QTest::addColumn<unsigned>("bytes");
+    QTest::addColumn<int>("status");
+    for (int order = 0; order < 2; ++order) {
+        const unsigned start = order == 0 ? 0U : 7U;
+        const auto prefix = QByteArray::number(order);
+        QTest::newRow((prefix + "-zero").constData()) << order << start << 0U << 1U << int(SignalDecodeStatus::InvalidDefinition);
+        QTest::newRow((prefix + "-65").constData()) << order << start << 65U << 9U << int(SignalDecodeStatus::InvalidDefinition);
+        QTest::newRow((prefix + "-empty").constData()) << order << start << 8U << 0U << int(SignalDecodeStatus::InsufficientPayload);
+        QTest::newRow((prefix + "-short").constData()) << order << start << 16U << 1U << int(SignalDecodeStatus::InsufficientPayload);
+        QTest::newRow((prefix + "-large-start").constData()) << order << std::numeric_limits<unsigned>::max() << 8U << 1U << int(SignalDecodeStatus::InsufficientPayload);
+    }
+}
+
+void CoverageTest::invalidSignalStatus() {
+    QFETCH(int, order); QFETCH(unsigned, start); QFETCH(unsigned, length);
+    QFETCH(unsigned, bytes); QFETCH(int, status);
+    DecodeSignal signal;
+    signal.startBit = start; signal.length = length;
+    signal.byteOrder = order == 0 ? ByteOrder::Intel : ByteOrder::Motorola;
+    const auto database = SingleSignal(signal);
+    RawCanFrame raw; raw.canId = 17U; raw.data.assign(bytes, 255U);
+    const auto decoded = DbcDecoder().Decode(database, raw);
+    QVERIFY(decoded.valid);
+    QVERIFY(!decoded.signals[0].valid);
+    QCOMPARE(int(decoded.signals[0].status), status);
+    QVERIFY(decoded.signals[0].GetValueDescription() == nullptr);
+}
+
+void CoverageTest::malformedRuntimeMultiplexing_data() {
+    QTest::addColumn<int>("kind");
+    QTest::newRow("two-selectors") << 0;
+    QTest::newRow("signed-selector") << 1;
+    QTest::newRow("65-bit-selector") << 2;
+    QTest::newRow("branch-out-of-range") << 3;
+}
+
+void CoverageTest::malformedRuntimeMultiplexing() {
+    QFETCH(int, kind);
+    DecodeSignal selector; selector.length = 1U; selector.multiplexing.role = MultiplexRole::Selector;
+    auto database = SingleSignal(selector);
+    DecodeSignal branch; branch.startBit = 8U; branch.length = 8U;
+    branch.multiplexing.role = MultiplexRole::Branch; branch.multiplexing.value = 1U;
+    database.frames[0].signals.push_back(branch);
+    DecodeSignal ordinary; ordinary.startBit = 16U; ordinary.length = 8U;
+    database.frames[0].signals.push_back(ordinary);
+    if (kind == 0) database.frames[0].signals.push_back(selector);
+    if (kind == 1) database.frames[0].signals[0].valueType = ValueType::Signed;
+    if (kind == 2) database.frames[0].signals[0].length = 65U;
+    if (kind == 3) database.frames[0].signals[1].multiplexing.value = 2U;
+    RawCanFrame raw; raw.canId = 17U; raw.data = {1U, 42U, 99U};
+    const auto result = DbcDecoder().Decode(database, raw);
+    QCOMPARE(int(result.signals[1].status), int(SignalDecodeStatus::InvalidDefinition));
+    QVERIFY(!result.signals[1].valid);
+    QVERIFY(result.signals[2].valid);
+    QCOMPARE(std::get<std::uint64_t>(result.signals[2].rawValue), std::uint64_t(99));
+    if (kind != 3) {
+        QCOMPARE(int(result.signals[0].status), int(SignalDecodeStatus::InvalidDefinition));
+        if (kind == 0) QCOMPARE(int(result.signals[3].status), int(SignalDecodeStatus::InvalidDefinition));
+    }
+}
+
+void CoverageTest::pgn_data() {
+    QTest::addColumn<unsigned>("id"); QTest::addColumn<unsigned>("expected"); QTest::addColumn<bool>("hasPgn");
+    QTest::newRow("standard") << 0x7FFU << 0U << false;
+    for (unsigned dp : {0U, 1U})
+        for (unsigned pf : {239U, 240U})
+            for (unsigned ps : {0U, 0xABU}) {
+                const unsigned id = 0x80000000U | (dp << 24U) | (pf << 16U) | (ps << 8U) | 0x42U;
+                const unsigned expected = (dp << 16U) | (pf == 239U ? 0xEF00U : 0xF000U | ps);
+                const auto name = QByteArray::number(dp) + "-" + QByteArray::number(pf) + "-" + QByteArray::number(ps);
+                QTest::newRow(name.constData()) << id << expected << true;
+            }
+}
+
+void CoverageTest::pgn() {
+    QFETCH(unsigned, id); QFETCH(unsigned, expected); QFETCH(bool, hasPgn);
+    const auto parsed = ParseText("BO_ " + std::to_string(id) + " Frame: 8 ECU\n");
+    QCOMPARE(parsed.frames[0].hasPgn, hasPgn);
+    QCOMPARE(parsed.frames[0].pgn, expected);
+}
+
+void CoverageTest::comments_data() {
+    QTest::addColumn<QString>("before"); QTest::addColumn<QString>("after");
+    QTest::addColumn<QString>("frameComment"); QTest::addColumn<QString>("signalComment");
+    QTest::newRow("tabs") << QString::fromUtf8("") << QString::fromUtf8("CM_\tBO_ 1 \"Frame\";\nCM_\tSG_ 1 State \"Signal\";\n") << QString::fromUtf8("Frame") << QString::fromUtf8("Signal");
+    QTest::newRow("empty-overwrite") << QString::fromUtf8("") << QString::fromUtf8("CM_ BO_ 1 \"Old\";\nCM_ BO_ 1 \"\";\nCM_ SG_ 1 State \"Old\";\nCM_ SG_ 1 State \"\";\n") << QString::fromUtf8("") << QString::fromUtf8("");
+    QTest::newRow("last-wins") << QString::fromUtf8("") << QString::fromUtf8("CM_ BO_ 1 \"First\";\nCM_ BO_ 1 \"Last\";\nCM_ SG_ 1 State \"First\";\nCM_ SG_ 1 State \"Last\";\n") << QString::fromUtf8("Last") << QString::fromUtf8("Last");
+    QTest::newRow("missing-targets") << QString::fromUtf8("") << QString::fromUtf8("CM_ BO_ 2 \"Unknown\";\nCM_ SG_ 2 State \"Unknown\";\nCM_ SG_ 1 Missing \"Unknown\";\n") << QString::fromUtf8("") << QString::fromUtf8("");
+    // Current documented limitation: comments resolve only already parsed targets.
+    QTest::newRow("before-definitions") << QString::fromUtf8("CM_ BO_ 1 \"Early\";\nCM_ SG_ 1 State \"Early\";\n") << QString::fromUtf8("") << QString::fromUtf8("") << QString::fromUtf8("");
+    QTest::newRow("missing-quotes") << QString::fromUtf8("") << QString::fromUtf8("CM_ BO_ 1 Missing;\nCM_ SG_ 1 State \"Unclosed;\n") << QString::fromUtf8("") << QString::fromUtf8("");
+}
+
+void CoverageTest::comments() {
+    QFETCH(QString, before); QFETCH(QString, after); QFETCH(QString, frameComment); QFETCH(QString, signalComment);
+    const auto parsed = ParseText(before.toStdString() + "BO_ 1 Frame: 1 ECU\nSG_ State : 0|8@1+ (1,0) [0|255] \"\" ECU\n" + after.toStdString());
+    QCOMPARE(parsed.frames[0].comment, frameComment.toStdString());
+    QCOMPARE(parsed.frames[0].signals[0].comment, signalComment.toStdString());
+}
+
+void CoverageTest::fileFormatting_data() {
+    QTest::addColumn<QString>("text"); QTest::addColumn<unsigned>("frames");
+    QTest::newRow("empty") << QString::fromUtf8("") << 0U;
+    QTest::newRow("whitespace") << QString::fromUtf8(" \t\r\n\n\t") << 0U;
+    QTest::newRow("unknown-only") << QString::fromUtf8("VERSION \"test\"\nBU_: ECU\nUNKNOWN_ data\n") << 0U;
+    QTest::newRow("no-final-newline") << QString::fromUtf8("BO_ 1 Frame: 1 ECU\nSG_ State : 0|8@1+ (1,0) [0|255] \"\" ECU") << 1U;
+    QTest::newRow("crlf") << QString::fromUtf8("\r\nBO_ 1 Frame: 1 ECU\r\nSG_ State : 0|8@1+ (1,0) [0|255] \"\" ECU\r\nCM_ BO_ 1 \"Comment\";\r\nVAL_ 1 State 0 \"Off\";\r\n") << 1U;
+}
+
+void CoverageTest::fileFormatting() {
+    QFETCH(QString, text); QFETCH(unsigned, frames);
+    const auto parsed = ParseText(text.toStdString());
+    QCOMPARE(parsed.frames.size(), std::size_t(frames));
+    if (frames) {
+        QCOMPARE(parsed.frames[0].signals.size(), std::size_t(1));
+        if (text.contains("\r\nBO_")) {
+            QCOMPARE(parsed.frames[0].comment, std::string("Comment"));
+            const auto *description = FindValueDescription(parsed.frames[0].signals[0].valueDescriptions, std::uint64_t(0));
+            QVERIFY(description != nullptr);
+            QCOMPARE(*description, std::string("Off"));
+        }
+    }
+}
+
+void CoverageTest::missingFile() {
+    QTemporaryFile file;
+    QVERIFY(file.open());
+    const auto path = file.fileName();
+    QVERIFY(file.remove());
+    try { DbcParser().ParseFile(path.toStdString()); QFAIL("Missing file must throw"); }
+    catch (const std::runtime_error &error) {
+        QCOMPARE(std::string(error.what()), "Failed to open DBC file: " + path.toStdString());
+    }
+}
+
+void CoverageTest::builders() {
+    const auto emptyRuntime = DbcDecodeBuilder().Build(DbcDatabase());
+    QVERIFY(emptyRuntime.frames.empty());
+    QVERIFY(emptyRuntime.frameIndexByKey.empty());
+    const auto emptyTree = DbcTreeBuilder().Build(DbcDatabase());
+    QCOMPARE(emptyTree->GetType(), NodeType::Root);
+    QCOMPARE(emptyTree->GetName(), std::string("dbc"));
+    QCOMPARE(emptyTree->GetChildCount(), std::size_t(0));
+    QVERIFY(emptyTree->GetFrame() == nullptr && emptyTree->GetSignal() == nullptr);
+    const auto expected = ParseText(
+        "BO_ 256 Standard: 3 ECU1\n"
+        "SG_ Mode M : 0|8@1+ (2,3) [0|513] \"mode\" ECU1,ECU2\n"
+        "SG_ Branch m1 : 15|8@0- (-2,5) [-249|261] \"rpm\" ECU2,ECU3\n"
+        "SG_ Always : 16|8@1+ (0.25,-1) [-1|62.75] \"V\" ECU3\n"
+        "CM_ BO_ 256 \"Frame comment\";\nCM_ SG_ 256 Branch \"Branch comment\";\n"
+        "VAL_ 256 Branch -1 \"Negative\" 1 \"Positive\";\n"
+        "BO_ 2163212866 Extended: 8 ECU4\n");
+    DecodeDatabase runtime;
+    std::unique_ptr<TreeNode> tree;
+    {
+        DbcDatabase source = expected;
+        runtime = DbcDecodeBuilder().Build(source);
+        tree = DbcTreeBuilder().Build(source);
+        source.frames[0].name = "Changed";
+        source.frames[0].signals[1].receivers.clear();
+        source.frames[0].signals[1].valueDescriptions.clear();
+        source.frames.clear();
+    }
+    QCOMPARE(runtime.frames.size(), expected.frames.size());
+    QCOMPARE(tree->GetChildCount(), expected.frames.size());
+    QCOMPARE(runtime.frameIndexByKey.size(), expected.frames.size());
+    for (std::size_t i = 0; i < expected.frames.size(); ++i) {
+        const FrameInfo &frame = expected.frames[i];
+        const DecodeFrame &decodedFrame = runtime.frames[i];
+        const TreeNode *node = tree->GetChild(i);
+        QVERIFY(node && node->GetFrame());
+        QCOMPARE(node->GetType(), NodeType::Frame);
+        QCOMPARE(node->GetName(), frame.name);
+        QVERIFY(node->GetSignal() == nullptr);
+        QCOMPARE(runtime.frameIndexByKey.at(FrameKey(frame.canId, frame.isExtended)), i);
+        const FrameInfo &copied = *node->GetFrame();
+        QCOMPARE(copied.name, frame.name); QCOMPARE(decodedFrame.name, frame.name);
+        QCOMPARE(copied.canId, frame.canId); QCOMPARE(decodedFrame.canId, frame.canId);
+        QCOMPARE(copied.isExtended, frame.isExtended); QCOMPARE(decodedFrame.isExtended, frame.isExtended);
+        QCOMPARE(copied.dlc, frame.dlc); QCOMPARE(decodedFrame.dlc, frame.dlc);
+        QCOMPARE(copied.pgn, frame.pgn); QCOMPARE(decodedFrame.pgn, frame.pgn);
+        QCOMPARE(copied.hasPgn, frame.hasPgn); QCOMPARE(decodedFrame.hasPgn, frame.hasPgn);
+        QCOMPARE(copied.transmitter, frame.transmitter); QCOMPARE(decodedFrame.transmitter, frame.transmitter);
+        QCOMPARE(copied.comment, frame.comment); QCOMPARE(decodedFrame.comment, frame.comment);
+        QCOMPARE(node->GetChildCount(), frame.signals.size());
+        QCOMPARE(copied.signals.size(), frame.signals.size());
+        QCOMPARE(decodedFrame.signals.size(), frame.signals.size());
+        for (std::size_t j = 0; j < frame.signals.size(); ++j) {
+            const auto &original = frame.signals[j];
+            const auto &target = decodedFrame.signals[j];
+            const auto *leaf = node->GetChild(j);
+            QVERIFY(leaf && leaf->GetSignal());
+            QCOMPARE(leaf->GetType(), NodeType::Signal);
+            QCOMPARE(leaf->GetName(), original.name);
+            QVERIFY(leaf->GetFrame() == nullptr);
+            // Check both the frame payload copy and each child payload copy.
+            for (const SignalInfo *copy : {&copied.signals[j], leaf->GetSignal()}) {
+                QCOMPARE(copy->name, original.name); QCOMPARE(copy->startBit, original.startBit);
+                QCOMPARE(copy->length, original.length); QCOMPARE(copy->isLittleEndian, original.isLittleEndian);
+                QCOMPARE(copy->isSigned, original.isSigned); QCOMPARE(copy->factor, original.factor);
+                QCOMPARE(copy->offset, original.offset); QCOMPARE(copy->minimum, original.minimum);
+                QCOMPARE(copy->maximum, original.maximum); QCOMPARE(copy->unit, original.unit);
+                QCOMPARE(copy->comment, original.comment); QVERIFY(copy->receivers == original.receivers);
+                QVERIFY(copy->valueDescriptions == original.valueDescriptions);
+                QCOMPARE(copy->multiplexing.role, original.multiplexing.role);
+                QCOMPARE(copy->multiplexing.value, original.multiplexing.value);
+            }
+            QCOMPARE(target.name, original.name); QCOMPARE(target.startBit, original.startBit);
+            QCOMPARE(target.length, original.length);
+            QCOMPARE(target.byteOrder, original.isLittleEndian ? ByteOrder::Intel : ByteOrder::Motorola);
+            QCOMPARE(target.valueType, original.isSigned ? ValueType::Signed : ValueType::Unsigned);
+            QCOMPARE(target.factor, original.factor); QCOMPARE(target.offset, original.offset);
+            QCOMPARE(target.minimum, original.minimum); QCOMPARE(target.maximum, original.maximum);
+            QCOMPARE(target.unit, original.unit); QCOMPARE(target.comment, original.comment);
+            QVERIFY(target.receivers == original.receivers);
+            QVERIFY(target.valueDescriptions == original.valueDescriptions);
+            QCOMPARE(target.multiplexing.role, original.multiplexing.role);
+            QCOMPARE(target.multiplexing.value, original.multiplexing.value);
+        }
+    }
+}
+
+void CoverageTest::physicalConversion_data() {
+    QTest::addColumn<double>("factor"); QTest::addColumn<double>("offset"); QTest::addColumn<double>("expected");
+    QTest::newRow("zero-factor") << 0.0 << 7.0 << 7.0;
+    QTest::newRow("negative-factor") << -2.0 << 5.0 << -15.0;
+    QTest::newRow("above-declared-range") << 2.0 << 3.0 << 23.0;
+}
+
+void CoverageTest::physicalConversion() {
+    QFETCH(double, factor); QFETCH(double, offset); QFETCH(double, expected);
+    DecodeSignal signal; signal.length = 8U; signal.factor = factor; signal.offset = offset;
+    signal.minimum = 0.0; signal.maximum = 1.0;
+    const auto database = SingleSignal(signal);
+    RawCanFrame raw; raw.canId = 17U; raw.data = {10U};
+    const auto decoded = DbcDecoder().Decode(database, raw);
+    QVERIFY(decoded.signals[0].valid);
+    QCOMPARE(std::get<std::uint64_t>(decoded.signals[0].rawValue), std::uint64_t(10));
+    QCOMPARE(decoded.signals[0].physicalValue, expected);
+}
+
+void CoverageTest::multiplexingScenarios() {
+    const auto selectorOnly = DbcDecodeBuilder().Build(ParseText(
+        "BO_ 1 Frame: 1 ECU\nSG_ Mode M : 0|1@1+ (1,0) [0|1] \"\" ECU\n"));
+    RawCanFrame raw; raw.canId = 1U; raw.data = {1U};
+    const auto only = DbcDecoder().Decode(selectorOnly, raw);
+    QCOMPARE(only.signals.size(), std::size_t(1));
+    QVERIFY(only.signals[0].valid);
+    const auto database = DbcDecodeBuilder().Build(ParseText(
+        "BO_ 1 First: 3 ECU\n"
+        "SG_ Mode M : 0|1@1+ (1,0) [0|1] \"\" ECU\n"
+        "SG_ A m0 : 8|8@1+ (1,0) [0|255] \"\" ECU\n"
+        "SG_ B m0 : 16|8@1+ (1,0) [0|255] \"\" ECU\n"
+        "BO_ 2 Second: 2 ECU\n"
+        "SG_ Mode M : 0|1@1+ (1,0) [0|1] \"\" ECU\n"
+        "SG_ A m1 : 8|8@1+ (1,0) [0|255] \"\" ECU\n"));
+    raw.data = {0U, 42U, 99U};
+    const auto first = DbcDecoder().Decode(database, raw);
+    QVERIFY(first.signals[1].valid && first.signals[2].valid);
+    QCOMPARE(std::get<std::uint64_t>(first.signals[1].rawValue), std::uint64_t(42));
+    QCOMPARE(std::get<std::uint64_t>(first.signals[2].rawValue), std::uint64_t(99));
+    raw.canId = 2U;
+    const auto secondInactive = DbcDecoder().Decode(database, raw);
+    QCOMPARE(secondInactive.signals[1].status, SignalDecodeStatus::Inactive);
+    raw.data[0] = 1U;
+    QVERIFY(DbcDecoder().Decode(database, raw).signals[1].valid);
+    raw.canId = 1U;
+    const auto firstInactive = DbcDecoder().Decode(database, raw);
+    QCOMPARE(firstInactive.signals[1].status, SignalDecodeStatus::Inactive);
+    QCOMPARE(firstInactive.signals[2].status, SignalDecodeStatus::Inactive);
+}
+
+void CoverageTest::multiplexingErrorLocations_data() {
+    QTest::addColumn<QString>("text"); QTest::addColumn<unsigned>("line"); QTest::addColumn<QString>("message");
+    const QString header = "BO_ 1 Frame: 3 ECU\n\n";
+    const QString selector = "SG_ Mode M : 0|1@1+ (1,0) [0|1] \"\" ECU\n";
+    const QString branch = "SG_ A m1 : 8|8@1+ (1,0) [0|255] \"\" ECU\n";
+    QTest::newRow("missing-selector") << header + branch << 3U << QString::fromUtf8("Multiplexed branch has no selector.");
+    QTest::newRow("second-selector") << header + selector + "\nSG_ Other M : 16|1@1+ (1,0) [0|1] \"\" ECU\n" << 5U << QString::fromUtf8("Multiplexing requires one unsigned selector per frame.");
+    QTest::newRow("signed-selector") << header + "SG_ Mode M : 0|1@1- (1,0) [-1|0] \"\" ECU\n" << 3U << QString::fromUtf8("Multiplexing requires one unsigned selector per frame.");
+    QTest::newRow("branch-range") << header + "SG_ A m2 : 8|8@1+ (1,0) [0|255] \"\" ECU\n" + selector << 3U << QString::fromUtf8("Branch value exceeds selector raw range.");
+    QTest::newRow("same-branch-overlap") << header + selector + branch + "SG_ B m1 : 15|8@0+ (1,0) [0|255] \"\" ECU\n" << 5U << QString::fromUtf8("Signals overlap without mutually exclusive multiplexing conditions.");
+    QTest::newRow("selector-overlap") << header + selector + "SG_ A m1 : 0|1@1+ (1,0) [0|1] \"\" ECU\n" << 4U << QString::fromUtf8("Signals overlap without mutually exclusive multiplexing conditions.");
+    QTest::newRow("unconditional-overlap") << header + selector + branch + "SG_ Always : 8|8@1+ (1,0) [0|255] \"\" ECU\n" << 5U << QString::fromUtf8("Signals overlap without mutually exclusive multiplexing conditions.");
+    QTest::newRow("ordinary-overlap") << header + "SG_ A : 8|8@1+ (1,0) [0|255] \"\" ECU\nSG_ B : 15|8@0+ (1,0) [0|255] \"\" ECU\n" << 4U << QString::fromUtf8("Signals overlap without mutually exclusive multiplexing conditions.");
+    QTest::newRow("extended-multiplexing") << header + "SG_MUL_VAL_ 1 A Mode 1-2;\n" << 3U << QString::fromUtf8("Extended and nested multiplexing are unsupported.");
+    QTest::newRow("nested-marker") << header + "SG_ A m1M : 8|8@1+ (1,0) [0|255] \"\" ECU\n" << 3U << QString::fromUtf8("Invalid or unsupported multiplexing marker.");
+}
+
+void CoverageTest::multiplexingErrorLocations() {
+    QFETCH(QString, text); QFETCH(unsigned, line); QFETCH(QString, message);
+    QTemporaryFile file; QVERIFY(file.open());
+    const QByteArray content = text.toUtf8();
+    QCOMPARE(file.write(content), qint64(content.size())); QVERIFY(file.flush());
+    try { DbcParser().ParseFile(file.fileName().toStdString()); QFAIL("Expected multiplexing rejection"); }
+    catch (const std::runtime_error &error) {
+        QCOMPARE(QString::fromStdString(error.what()), file.fileName() + ":" + QString::number(line) + ": " + message);
+    }
+}
+
+void CoverageTest::escapedValueDescriptions() {
+    const auto parsed = ParseText(
+        "BO_ 1 Frame: 1 ECU\nSG_ State : 0|8@1+ (1,0) [0|255] \"\" ECU\n"
+        R"dbc(VAL_ 1 State -0 "Ноль" 1 "C:\\trace" 2 "\\\"quoted\"\\";)dbc" "\n");
+    const auto &values = parsed.frames[0].signals[0].valueDescriptions;
+    QCOMPARE(values.size(), std::size_t(3));
+    QVERIFY(values.find(RawSignalValue(std::int64_t(0))) == values.end());
+    const auto *zero = FindValueDescription(values, std::int64_t(0));
+    const auto *path = FindValueDescription(values, std::uint64_t(1));
+    const auto *quoted = FindValueDescription(values, std::uint64_t(2));
+    QVERIFY(zero && path && quoted);
+    QCOMPARE(*zero, std::string("Ноль"));
+    QCOMPARE(*path, std::string("C:\\trace"));
+    QCOMPARE(*quoted, std::string("\\\"quoted\"\\"));
+    QVERIFY(NormalizeValueKey(RawSignalValue(std::int64_t(0))) == RawSignalValue(std::uint64_t(0)));
+    QVERIFY(NormalizeValueKey(RawSignalValue(std::int64_t(-1))) == RawSignalValue(std::int64_t(-1)));
+}
+
+void CoverageTest::factory() {
+    TypeFactory<std::string, FactoryBase, std::unique_ptr<int>> factory;
+    QVERIFY(!factory.contains("value"));
+    QVERIFY_THROWS_EXCEPTION(std::out_of_range, static_cast<void>(factory.creator("missing")));
+    QVERIFY_THROWS_EXCEPTION(std::out_of_range, static_cast<void>(factory.create("missing", std::make_unique<int>(1))));
+    factory.registerType<FactoryFirst>("value");
+    QVERIFY(factory.contains("value"));
+    auto argument = std::make_unique<int>(42);
+    const auto first = factory.create("value", std::move(argument));
+    QVERIFY(argument == nullptr);
+    QCOMPARE(first->Value(), 42);
+    const auto creator = factory.creator("value");
+    QCOMPARE(creator(std::make_unique<int>(7))->Value(), 7);
+    factory.registerType<FactorySecond>("value");
+    QCOMPARE(factory.create("value", std::make_unique<int>(42))->Value(), 43);
+    QCOMPARE(first->Value(), 42);
+    QCOMPARE(creator(std::make_unique<int>(7))->Value(), 7);
+}
+
+int RunCoverageTests(int argc, char **argv) {
+    CoverageTest tests;
+    return QTest::qExec(&tests, argc, argv);
+}
+#include "dbc_coverage_test.moc"
diff --git a/tests/dbc_tree_model_test.cpp b/tests/dbc_tree_model_test.cpp
index 068f515..37794b8 100644
--- a/tests/dbc_tree_model_test.cpp
+++ b/tests/dbc_tree_model_test.cpp
@@ -4,6 +4,7 @@
 #include <QAbstractItemModelTester>
 #include <QSignalSpy>
 #include <QTemporaryFile>
+#include <QStringList>
 #include <QtTest>
 #include <limits>
 
@@ -22,6 +23,76 @@ static std::unique_ptr<TreeNode> ParsedTree() {
 class ModelTest : public QObject {
     Q_OBJECT
 private Q_SLOTS:
+    void additionalMetadata() {
+        DbcDatabase database;
+        FrameInfo frame;
+        frame.name = "Extended";
+        frame.canId = 0x18F00442U;
+        frame.isExtended = true;
+        frame.dlc = 8U;
+        frame.comment = "Frame tooltip";
+        SignalInfo signal;
+        signal.name = "SignedMotorola";
+        signal.startBit = 7U;
+        signal.length = 16U;
+        signal.isLittleEndian = false;
+        signal.isSigned = true;
+        signal.unit = "rpm";
+        signal.comment = "Signal tooltip";
+        frame.signals.push_back(signal);
+        database.frames.push_back(frame);
+        DbcTreeModel model;
+        model.SetTree(DbcTreeBuilder().Build(database));
+        const QModelIndex parent = model.index(0, 0);
+        QCOMPARE(model.data(model.index(0, DbcTreeModel::ByteOrder, parent)).toString(), QString("Motorola"));
+        QCOMPARE(model.data(model.index(0, DbcTreeModel::Signed, parent)).toString(), QString("Signed"));
+        QCOMPARE(model.data(model.index(0, DbcTreeModel::CanId)).toString(), QString("0X18F00442"));
+        const QStringList headers = {"Name", "CAN ID", "Payload (bytes)", "Start bit",
+                                     "Length (bits)", "Byte order", "Signedness", "Unit", "Comment"};
+        for (int column = 0; column < model.columnCount(); ++column) {
+            const auto frameIndex = model.index(0, column);
+            const auto signalIndex = model.index(0, column, parent);
+            QCOMPARE(model.headerData(column, Qt::Horizontal).toString(), headers.at(column));
+            QVERIFY(!model.headerData(column, Qt::Horizontal, Qt::ToolTipRole).isValid());
+            QCOMPARE(model.data(frameIndex, Qt::ToolTipRole).toString(), QString("Frame tooltip"));
+            QCOMPARE(model.data(signalIndex, Qt::ToolTipRole).toString(), QString("Signal tooltip"));
+            QCOMPARE(model.data(frameIndex, DbcTreeModel::CommentRole).toString(), QString("Frame tooltip"));
+            QCOMPARE(model.data(signalIndex, DbcTreeModel::CommentRole).toString(), QString("Signal tooltip"));
+            QCOMPARE(model.data(frameIndex, DbcTreeModel::CanIdRole).toUInt(), frame.canId);
+            QCOMPARE(model.data(frameIndex, DbcTreeModel::PayloadLengthRole).toInt(), 8);
+            QCOMPARE(model.data(frameIndex, DbcTreeModel::ExtendedRole).toBool(), true);
+            QCOMPARE(model.data(signalIndex, DbcTreeModel::StartBitRole).toUInt(), 7U);
+            QCOMPARE(model.data(signalIndex, DbcTreeModel::BitLengthRole).toUInt(), 16U);
+            QCOMPARE(model.data(signalIndex, DbcTreeModel::LittleEndianRole).toBool(), false);
+            QCOMPARE(model.data(signalIndex, DbcTreeModel::SignedRole).toBool(), true);
+            QCOMPARE(model.data(signalIndex, DbcTreeModel::UnitRole).toString(), QString("rpm"));
+            const auto descriptions = model.data(signalIndex, DbcTreeModel::ValueDescriptionsRole);
+            QVERIFY(descriptions.isValid());
+            QVERIFY(descriptions.toList().isEmpty());
+            QVERIFY(!model.data(frameIndex, Qt::UserRole + 1000).isValid());
+            QVERIFY(!model.data(signalIndex, Qt::UserRole + 1000).isValid());
+            QVERIFY(!model.setData(frameIndex, "Changed", Qt::EditRole));
+            QVERIFY(!model.setData(signalIndex, "Changed", Qt::EditRole));
+        }
+        QCOMPARE(model.data(parent).toString(), QString("Extended"));
+        QCOMPARE(model.data(model.index(0, 0, parent)).toString(), QString("SignedMotorola"));
+    }
+    void emptyRootAndRejectedReplacement() {
+        DbcTreeModel model;
+        QAbstractItemModelTester tester(&model, QAbstractItemModelTester::FailureReportingMode::QtTest);
+        model.SetTree(ParsedTree());
+        QPersistentModelIndex retained(model.index(0, 0));
+        QSignalSpy resets(&model, &QAbstractItemModel::modelReset);
+        QVERIFY_THROWS_EXCEPTION(std::invalid_argument, model.SetTree(std::make_unique<TreeNode>(SignalInfo())));
+        QCOMPARE(resets.count(), 0);
+        QVERIFY(retained.isValid());
+        QCOMPARE(model.rowCount(), 2);
+        model.SetTree(DbcTreeBuilder().Build(DbcDatabase()));
+        QCOMPARE(resets.count(), 1);
+        QVERIFY(!retained.isValid());
+        QCOMPARE(model.rowCount(), 0);
+        QVERIFY(!model.index(0, 0).isValid());
+    }
     void navigation() {
         DbcTreeModel model;
         QAbstractItemModelTester tester(&model, QAbstractItemModelTester::FailureReportingMode::QtTest);
diff --git a/tests/main.cpp b/tests/main.cpp
index b5a388a..b93038d 100644
--- a/tests/main.cpp
+++ b/tests/main.cpp
@@ -3,10 +3,12 @@
 
 int RunParserTests(int argc, char **argv);
 int RunDecoderTests(int argc, char **argv);
+int RunCoverageTests(int argc, char **argv);
 
 int main(int argc, char **argv) {
     QCoreApplication application(argc, argv);
     const int parserResult = RunParserTests(argc, argv);
     const int decoderResult = RunDecoderTests(argc, argv);
-    return parserResult | decoderResult;
+    const int coverageResult = RunCoverageTests(argc, argv);
+    return parserResult | decoderResult | coverageResult;
 }
diff --git a/tests/tests.pro b/tests/tests.pro
index f5d428d..13abad9 100644
--- a/tests/tests.pro
+++ b/tests/tests.pro
@@ -7,5 +7,5 @@ CONFIG -= app_bundle
 include(../core/core.pri)
 include(parser_tests.pri)
 include(decoder_tests.pri)
-SOURCES += main.cpp
+SOURCES += main.cpp dbc_coverage_test.cpp
 CONFIG -= debug_and_release debug_and_release_target