Import the results of other test frameworks

Tests Catch3 does not run had no history, flaky detection or quarantine.
--import=FILE reads a report instead of running tests and sends it through
the analysis, history and reports of a run: JUnit with Surefire's reruns,
xUnit.net v2, TRX, TAP 12 to 14, CTRF, Catch3's own --json report and
catch3-results, a small JSON Lines format for tools with none of these.

Results that share an identifier are attempts at one test, so a report of a
rerun gives a flaky test. --import-revision says what was tested: a verdict
that changes on one revision also counts as flaky. --import-name keeps the
results in a history of their own, which --analytics reads too. A TAP stream
that ends early fails instead of reading as a run that passed.

The amalgamation script now accepts a relative include of the third-party
wrappers, because pugixml is included from a second directory.

15 files changed, 1858 insertions, 96 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index aee8c7a3..87b19651 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -310,6 +310,7 @@ set(PROGMASOFT_RUNNER_FILES
   "${CATCH_DIR}/src/Progmasoft/Runner/Process.hpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/ProjectConfig.hpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/Protocol.hpp"
+  "${CATCH_DIR}/src/Progmasoft/Runner/ResultImport.hpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/ResultsJson.hpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/Scheduler.hpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/SchedulerModel.hpp"
@@ -329,6 +330,10 @@ set(PROGMASOFT_RUNNER_FILES
   "${CATCH_DIR}/src/Progmasoft/Runner/Process.cpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/ProjectConfig.cpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/Protocol.cpp"
+  "${CATCH_DIR}/src/Progmasoft/Runner/ResultImport.cpp"
+  "${CATCH_DIR}/src/Progmasoft/Runner/ResultImportJson.cpp"
+  "${CATCH_DIR}/src/Progmasoft/Runner/ResultImportTap.cpp"
+  "${CATCH_DIR}/src/Progmasoft/Runner/ResultImportXml.cpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/ResultsJson.cpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/Runner.cpp"
   "${CATCH_DIR}/src/Progmasoft/Runner/Scheduler.cpp"
diff --git a/src/Progmasoft/Catch3/meson.build b/src/Progmasoft/Catch3/meson.build
index 7b75dc6d..ccf93f29 100644
--- a/src/Progmasoft/Catch3/meson.build
+++ b/src/Progmasoft/Catch3/meson.build
@@ -297,6 +297,10 @@ runner_sources = files(
   '../Runner/Process.cpp',
   '../Runner/ProjectConfig.cpp',
   '../Runner/Protocol.cpp',
+  '../Runner/ResultImport.cpp',
+  '../Runner/ResultImportJson.cpp',
+  '../Runner/ResultImportTap.cpp',
+  '../Runner/ResultImportXml.cpp',
   '../Runner/ResultsJson.cpp',
   '../Runner/Runner.cpp',
   '../Runner/Scheduler.cpp',
diff --git a/src/Progmasoft/PugiXml.inl b/src/Progmasoft/PugiXml.inl
index 207bd17f..e93dd679 100644
--- a/src/Progmasoft/PugiXml.inl
+++ b/src/Progmasoft/PugiXml.inl
@@ -1,8 +1,8 @@
 // Copyright (c) 2026 Progmasoft.
 // SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-2.0
 
-// pugixml, compiled header-only into XmlWriter.cpp and nowhere else. Its
-// namespace is renamed, so Catch3 cannot collide with a copy of pugixml that
+// pugixml, compiled header-only into XmlWriter.cpp and ResultImportXml.cpp
+// and nowhere else. Its namespace is renamed, so Catch3 cannot collide with a copy of pugixml that
 // the tests themselves link. It is vendored code: it is read as a system
 // header, outside the warnings Catch3 builds with.
 #if defined(__GNUC__) || defined(__clang__)
diff --git a/src/Progmasoft/Runner/Analysis.cpp b/src/Progmasoft/Runner/Analysis.cpp
index 802f1ed9..739ca2dc 100644
--- a/src/Progmasoft/Runner/Analysis.cpp
+++ b/src/Progmasoft/Runner/Analysis.cpp
@@ -350,6 +350,11 @@ namespace Progmasoft::Catch3::Runner
             test.analysis.insert(
                 test.analysis.end(), findings.begin(), findings.end());
 
+            // An imported failure ran somewhere else.
+            if (inputs.program.empty())
+            {
+                continue;
+            }
             std::string replay = QuoteArgument(inputs.program) + " " +
                                  QuoteArgument(QuoteTestSpec(test.name)) +
                                  " --seed=" + std::to_string(failure->seed);
diff --git a/src/Progmasoft/Runner/Console.cpp b/src/Progmasoft/Runner/Console.cpp
index 44765311..91691967 100644
--- a/src/Progmasoft/Runner/Console.cpp
+++ b/src/Progmasoft/Runner/Console.cpp
@@ -203,6 +203,21 @@ namespace Progmasoft::Catch3::Runner
     }
 
     void
+    ConsoleReport::ImportStarting(std::size_t tests, std::size_t files)
+    {
+        total_ = tests;
+        if (options_.verbosity == Verbosity::kQuiet)
+        {
+            return;
+        }
+        Write(output_,
+              Paint("Catch3", kBold) + ": " + std::to_string(tests)
+                  + " test(s) imported from " + std::to_string(files)
+                  + " report(s)\n");
+        std::fflush(output_);
+    }
+
+    void
     ConsoleReport::Retrying(const TestResult &test, const Attempt &attempt)
     {
         if (options_.verbosity != Verbosity::kVerbose)
diff --git a/src/Progmasoft/Runner/Console.hpp b/src/Progmasoft/Runner/Console.hpp
index e79fcf68..32c83976 100644
--- a/src/Progmasoft/Runner/Console.hpp
+++ b/src/Progmasoft/Runner/Console.hpp
@@ -25,6 +25,10 @@ namespace Progmasoft::Catch3::Runner
                     std::uint32_t seed,
                     const std::vector<std::string> &notes);
 
+        /// The start of `--import`: results read from `files` reports.
+        void
+        ImportStarting(std::size_t tests, std::size_t files);
+
         void
         TestFinished(const TestResult &test);
 
diff --git a/src/Progmasoft/Runner/Options.cpp b/src/Progmasoft/Runner/Options.cpp
index c59d7e40..4ae99eb3 100644
--- a/src/Progmasoft/Runner/Options.cpp
+++ b/src/Progmasoft/Runner/Options.cpp
@@ -683,6 +683,58 @@ namespace Progmasoft::Catch3::Runner
                      options.replayFailures = true;
                      return Status::Ok();
                  }},
+                {"import",
+                 '\0',
+                 Takes::kValue,
+                 "FILE",
+                 "Importing results",
+                 "read a report of another framework instead of running tests "
+                 "(repeatable)",
+                 [](Options &options, const std::optional<std::string> &value) {
+                     options.mode = Mode::kImport;
+                     options.importFiles.push_back(*value);
+                     return Status::Ok();
+                 }},
+                {"import-format",
+                 '\0',
+                 Takes::kValue,
+                 "FORMAT",
+                 "Importing results",
+                 "auto (default), catch3, junit, xunit, trx, tap or ctrf",
+                 [](Options &options, const std::optional<std::string> &value) {
+                     return ReadChoice<ImportFormat>(
+                         value,
+                         "import-format",
+                         {{"auto", ImportFormat::kAuto},
+                          {"catch3", ImportFormat::kCatch3},
+                          {"junit", ImportFormat::kJUnit},
+                          {"xunit", ImportFormat::kXUnit},
+                          {"trx", ImportFormat::kTrx},
+                          {"tap", ImportFormat::kTap},
+                          {"ctrf", ImportFormat::kCtrf}},
+                         options.importFormat);
+                 }},
+                {"import-name",
+                 '\0',
+                 Takes::kValue,
+                 "NAME",
+                 "Importing results",
+                 "the history imported results go to (default: imported); "
+                 "--analytics reads it too",
+                 [](Options &options, const std::optional<std::string> &value) {
+                     options.importName = *value;
+                     return Status::Ok();
+                 }},
+                {"import-revision",
+                 '\0',
+                 Takes::kValue,
+                 "REVISION",
+                 "Importing results",
+                 "what the reports tested (default: the Git commit here)",
+                 [](Options &options, const std::optional<std::string> &value) {
+                     options.importRevision = *value;
+                     return Status::Ok();
+                 }},
                 {"analytics",
                  '\0',
                  Takes::kOptionalValue,
diff --git a/src/Progmasoft/Runner/Options.hpp b/src/Progmasoft/Runner/Options.hpp
index 15bba45e..9f7f826e 100644
--- a/src/Progmasoft/Runner/Options.hpp
+++ b/src/Progmasoft/Runner/Options.hpp
@@ -21,6 +21,8 @@ namespace Progmasoft::Catch3::Runner
         kListTests,
         kListTags,
         kAnalytics,
+        /// Read the reports of other test frameworks.
+        kImport,
         kHelp,
         kVersion,
         /// Internal: run tests on behalf of a runner, over the protocol.
@@ -78,6 +80,20 @@ namespace Progmasoft::Catch3::Runner
         kOff,
     };
 
+    /// The reports `--import` reads.
+    enum class ImportFormat : std::uint8_t
+    {
+        /// Whichever the contents show.
+        kAuto,
+        /// Catch3's own: `--json` reports and catch3-results JSON Lines.
+        kCatch3,
+        kJUnit,
+        kXUnit,
+        kTrx,
+        kTap,
+        kCtrf,
+    };
+
     enum class ColorMode : std::uint8_t
     {
         kAuto,
@@ -157,6 +173,15 @@ namespace Progmasoft::Catch3::Runner
         bool replayFailures = false;
         bool analyticsJson = false;
 
+        // Importing the reports of other frameworks.
+        std::vector<std::string> importFiles;
+        ImportFormat importFormat = ImportFormat::kAuto;
+        /// The history they go to; "imported" when empty.
+        std::string importName;
+        /// What was tested, so that a verdict that changes on one revision
+        /// counts as flaky; the Git commit here when empty.
+        std::string importRevision;
+
         // Output.
         Verbosity verbosity = Verbosity::kNormal;
         ColorMode color = ColorMode::kAuto;
diff --git a/src/Progmasoft/Runner/ProjectConfig.cpp b/src/Progmasoft/Runner/ProjectConfig.cpp
index 54f89d9c..e382b5c5 100644
--- a/src/Progmasoft/Runner/ProjectConfig.cpp
+++ b/src/Progmasoft/Runner/ProjectConfig.cpp
@@ -113,6 +113,10 @@ namespace Progmasoft::Catch3::Runner
             "break",
             "replay",
             "analytics",
+            "import",
+            "import-format",
+            "import-name",
+            "import-revision",
             "verbose",
             "quiet",
             "premature-exit-guard-file",
diff --git a/src/Progmasoft/Runner/ResultImport.cpp b/src/Progmasoft/Runner/ResultImport.cpp
new file mode 100644
index 00000000..10a9c5a8
--- /dev/null
+++ b/src/Progmasoft/Runner/ResultImport.cpp
@@ -0,0 +1,305 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-2.0
+#include <Progmasoft/Runner/History.hpp>
+#include <Progmasoft/Runner/Json.hpp>
+#include <Progmasoft/Runner/ResultImport.hpp>
+#include <algorithm>
+#include <cctype>
+#include <cmath>
+#include <iterator>
+#include <map>
+#include <utility>
+
+namespace Progmasoft::Catch3::Runner
+{
+    std::string_view
+    ImportTrim(std::string_view text)
+    {
+        const auto blank = [](char character) {
+            return std::isspace(static_cast<unsigned char>(character)) != 0;
+        };
+        while (!text.empty() && blank(text.front()))
+        {
+            text.remove_prefix(1);
+        }
+        while (!text.empty() && blank(text.back()))
+        {
+            text.remove_suffix(1);
+        }
+        return text;
+    }
+
+    bool
+    ImportStartsWith(std::string_view text, std::string_view prefix)
+    {
+        return text.substr(0, prefix.size()) == prefix;
+    }
+
+    std::vector<std::string_view>
+    ImportLines(std::string_view text)
+    {
+        std::vector<std::string_view> lines;
+        while (!text.empty())
+        {
+            const auto end = text.find('\n');
+            auto line = text.substr(0, end);
+            if (!line.empty() && line.back() == '\r')
+            {
+                line.remove_suffix(1);
+            }
+            lines.push_back(line);
+            if (end == std::string_view::npos)
+            {
+                break;
+            }
+            text.remove_prefix(end + 1);
+        }
+        return lines;
+    }
+
+    namespace
+    {
+        namespace ImportText
+        {
+            /// Without a byte order mark and the white space before the
+            /// first character that counts.
+            std::string_view
+            Contents(std::string_view text)
+            {
+                if (ImportStartsWith(text, "\xEF\xBB\xBF"))
+                {
+                    text.remove_prefix(3);
+                }
+                return ImportTrim(text);
+            }
+
+            /// The name of the root element of an XML document.
+            std::string_view
+            RootElement(std::string_view text)
+            {
+                while (!text.empty())
+                {
+                    const auto open = text.find('<');
+                    if (open == std::string_view::npos
+                        || open + 1 >= text.size())
+                    {
+                        return {};
+                    }
+                    text.remove_prefix(open + 1);
+                    if (text.front() == '?' || text.front() == '!')
+                    {
+                        const auto close = text.find('>');
+                        if (close == std::string_view::npos)
+                        {
+                            return {};
+                        }
+                        text.remove_prefix(close + 1);
+                        continue;
+                    }
+                    return text.substr(0, text.find_first_of(" \t\r\n/>"));
+                }
+                return {};
+            }
+        } // namespace ImportText
+    } // namespace
+
+    std::optional<ImportFormat>
+    DetectImportFormat(std::string_view text)
+    {
+        const std::string_view contents = ImportText::Contents(text);
+        if (contents.empty())
+        {
+            return std::nullopt;
+        }
+        if (contents.front() == '<')
+        {
+            const std::string_view root = ImportText::RootElement(contents);
+            if (root == "testsuites" || root == "testsuite")
+            {
+                return ImportFormat::kJUnit;
+            }
+            if (root == "assemblies" || root == "assembly")
+            {
+                return ImportFormat::kXUnit;
+            }
+            if (root == "TestRun")
+            {
+                return ImportFormat::kTrx;
+            }
+            return std::nullopt;
+        }
+        if (contents.front() == '{')
+        {
+            auto whole = ParseJson(contents);
+            if (!whole)
+            {
+                // JSON Lines: the first line says what the others are.
+                whole = ParseJson(contents.substr(0, contents.find('\n')));
+            }
+            return whole ? ImportJsonFormat(*whole) : std::nullopt;
+        }
+        for (const auto raw : ImportLines(contents))
+        {
+            const std::string_view line = ImportTrim(raw);
+            if (line.empty() || line.front() == '#')
+            {
+                continue;
+            }
+            if (ImportStartsWith(line, "TAP version")
+                || ImportStartsWith(line, "1..") || IsTapTestLine(line))
+            {
+                return ImportFormat::kTap;
+            }
+            break;
+        }
+        return std::nullopt;
+    }
+
+    Expected<std::vector<TestResult>>
+    ParseImport(std::string_view text, ImportFormat format)
+    {
+        const std::string_view contents = ImportText::Contents(text);
+        switch (format)
+        {
+            case ImportFormat::kAuto:
+                break;
+            case ImportFormat::kCatch3:
+                return ParseCatch3Report(contents);
+            case ImportFormat::kJUnit:
+                return ParseJUnit(contents);
+            case ImportFormat::kXUnit:
+                return ParseXUnit(contents);
+            case ImportFormat::kTrx:
+                return ParseTrx(contents);
+            case ImportFormat::kTap:
+                return ParseTap(contents);
+            case ImportFormat::kCtrf:
+                return ParseCtrf(contents);
+        }
+        const auto detected = DetectImportFormat(contents);
+        if (!detected)
+        {
+            return Error{ "its format is not one Catch3 knows; "
+                          "--import-format names it" };
+        }
+        return ParseImport(contents, *detected);
+    }
+
+    std::vector<TestResult>
+    MergeImported(std::vector<TestResult> results)
+    {
+        std::vector<TestResult> tests;
+        std::map<std::string, std::size_t> positions;
+        for (auto &result : results)
+        {
+            if (result.id.empty())
+            {
+                result.id = History::KeyOf(result);
+            }
+            const auto [position, added]
+                = positions.emplace(result.id, tests.size());
+            if (added)
+            {
+                tests.push_back(std::move(result));
+                continue;
+            }
+            TestResult &test = tests[position->second];
+            test.flaky = test.flaky || result.flaky;
+            std::move(result.attempts.begin(),
+                      result.attempts.end(),
+                      std::back_inserter(test.attempts));
+        }
+        for (auto &test : tests)
+        {
+            std::size_t passes = 0;
+            std::size_t failures = 0;
+            for (std::size_t index = 0; index < test.attempts.size(); ++index)
+            {
+                Attempt &attempt = test.attempts[index];
+                attempt.number = index + 1;
+                passes += attempt.outcome == Outcome::kPassed ? 1 : 0;
+                failures += IsFailure(attempt.outcome) ? 1 : 0;
+            }
+            if (test.attempts.empty())
+            {
+                continue;
+            }
+            test.outcome = test.attempts.back().outcome;
+            test.category = test.attempts.back().category;
+            if (passes > 0 && failures > 0)
+            {
+                test.outcome = Outcome::kPassed;
+                test.category = FailureCategory::kNone;
+                test.flaky = true;
+                test.analysis.push_back(
+                    "flaky: failed " + std::to_string(failures) + " of "
+                    + std::to_string(test.attempts.size()) + " attempts");
+            }
+        }
+        return tests;
+    }
+
+    TestResult
+    ImportedTest(std::string name, std::string className)
+    {
+        TestResult test;
+        test.name = std::move(name);
+        test.className = std::move(className);
+        test.id = History::KeyOf(test);
+        return test;
+    }
+
+    Attempt
+    ImportedAttempt(Outcome outcome,
+                    std::int64_t durationMicroseconds,
+                    std::string message,
+                    std::string details,
+                    FailureCategory category)
+    {
+        Attempt attempt;
+        attempt.outcome = outcome;
+        attempt.durationMicroseconds
+            = std::max<std::int64_t>(durationMicroseconds, 0);
+        if (outcome == Outcome::kSkipped)
+        {
+            attempt.standardOutput = std::move(message);
+            return attempt;
+        }
+        if (outcome != Outcome::kFailedAsExpected && !IsFailure(outcome))
+        {
+            return attempt;
+        }
+        if (category == FailureCategory::kNone)
+        {
+            category = outcome == Outcome::kCrashed ? FailureCategory::kCrash
+                       : outcome == Outcome::kTimedOut
+                           ? FailureCategory::kTimeout
+                           : FailureCategory::kAssertion;
+        }
+        if (message.empty())
+        {
+            message = details.substr(0, details.find('\n'));
+        }
+        attempt.category = category;
+        attempt.assertionsFailed = 1;
+        AssertionRecord assertion;
+        assertion.message = std::move(message);
+        assertion.expansion = std::move(details);
+        assertion.category = category;
+        assertion.allowed = outcome == Outcome::kFailedAsExpected;
+        attempt.assertions.push_back(std::move(assertion));
+        return attempt;
+    }
+
+    std::int64_t
+    ImportedMicroseconds(double seconds)
+    {
+        // About thirty years; a longer duration is not a duration.
+        constexpr double kLongest = 1e9;
+        if (!std::isfinite(seconds) || seconds <= 0.0 || seconds > kLongest)
+        {
+            return 0;
+        }
+        return static_cast<std::int64_t>(std::llround(seconds * 1e6));
+    }
+} // namespace Progmasoft::Catch3::Runner
diff --git a/src/Progmasoft/Runner/ResultImport.hpp b/src/Progmasoft/Runner/ResultImport.hpp
new file mode 100644
index 00000000..b9ddff27
--- /dev/null
+++ b/src/Progmasoft/Runner/ResultImport.hpp
@@ -0,0 +1,89 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-2.0
+#pragma once
+
+#include <Progmasoft/Catch3/Results.hpp>
+#include <cstdint>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include "Expected.hpp"
+#include "Json.hpp"
+#include "Options.hpp"
+
+namespace Progmasoft::Catch3::Runner
+{
+    /// The format of a report, from its contents; nothing when none fits.
+    [[nodiscard]] std::optional<ImportFormat>
+    DetectImportFormat(std::string_view text);
+
+    /// The results a report holds, in its order. A test the report names
+    /// twice comes back twice; `MergeImported` makes one test of them.
+    [[nodiscard]] Expected<std::vector<TestResult>>
+    ParseImport(std::string_view text, ImportFormat format);
+
+    /// One test per identifier: results that share one are attempts at that
+    /// test, in the order given, and the verdict is worked out over them. A
+    /// test that both failed and passed is flaky, as it is in a run of the
+    /// runner.
+    [[nodiscard]] std::vector<TestResult>
+    MergeImported(std::vector<TestResult> results);
+
+    /// A result without attempts yet.
+    [[nodiscard]] TestResult
+    ImportedTest(std::string name, std::string className);
+
+    /// One attempt as a report describes it. A failure gets an assertion
+    /// record with `message` and `details`, so the analysis treats it as it
+    /// treats a failure of Catch3's own; `category` defaults by outcome.
+    [[nodiscard]] Attempt
+    ImportedAttempt(Outcome outcome,
+                    std::int64_t durationMicroseconds,
+                    std::string message = {},
+                    std::string details = {},
+                    FailureCategory category = FailureCategory::kNone);
+
+    /// Seconds as a report gives them; what makes no sense as a duration
+    /// counts as zero.
+    [[nodiscard]] std::int64_t
+    ImportedMicroseconds(double seconds);
+
+    [[nodiscard]] std::string_view
+    ImportTrim(std::string_view text);
+
+    [[nodiscard]] bool
+    ImportStartsWith(std::string_view text, std::string_view prefix);
+
+    /// The lines of a text, without their line endings.
+    [[nodiscard]] std::vector<std::string_view>
+    ImportLines(std::string_view text);
+
+    /// A format of Catch3's own or CTRF, from a parsed document.
+    [[nodiscard]] std::optional<ImportFormat>
+    ImportJsonFormat(const JsonValue &value);
+
+    /// Whether a line reports a test in TAP.
+    [[nodiscard]] bool
+    IsTapTestLine(std::string_view line);
+
+    /// A `--json` report or catch3-results lines.
+    [[nodiscard]] Expected<std::vector<TestResult>>
+    ParseCatch3Report(std::string_view text);
+
+    [[nodiscard]] Expected<std::vector<TestResult>>
+    ParseCtrf(std::string_view text);
+
+    [[nodiscard]] Expected<std::vector<TestResult>>
+    ParseTap(std::string_view text);
+
+    [[nodiscard]] Expected<std::vector<TestResult>>
+    ParseJUnit(std::string_view text);
+
+    [[nodiscard]] Expected<std::vector<TestResult>>
+    ParseXUnit(std::string_view text);
+
+    [[nodiscard]] Expected<std::vector<TestResult>>
+    ParseTrx(std::string_view text);
+} // namespace Progmasoft::Catch3::Runner
diff --git a/src/Progmasoft/Runner/ResultImportJson.cpp b/src/Progmasoft/Runner/ResultImportJson.cpp
new file mode 100644
index 00000000..2cdc2019
--- /dev/null
+++ b/src/Progmasoft/Runner/ResultImportJson.cpp
@@ -0,0 +1,279 @@
+// Copyright (c) 2026 Progmasoft.
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-2.0
+
+// The JSON reports: Catch3's own and CTRF.
+#include <Progmasoft/Runner/Json.hpp>
+#include <Progmasoft/Runner/ResultImport.hpp>
+#include <Progmasoft/Runner/ResultsJson.hpp>
+#include <utility>
+
+namespace Progmasoft::Catch3::Runner
+{
+    namespace
+    {
+        namespace ImportJson
+        {
+            /// A format of Catch3's own or CTRF, from the parsed document.
+            std::optional<ImportFormat>
+            FormatOf(const JsonValue &value)
+            {
+                if (value["format"].AsString() == "catch3-run"
+                    || value["format"].AsString() == "catch3-results")
+                {
+                    return ImportFormat::kCatch3;
+                }
+                if (value["results"]["tests"].IsArray())
+                {
+                    return ImportFormat::kCtrf;
+                }
+                return std::nullopt;
+            }
+
+            /// What a test owes the verdict of an earlier run is worked out
+            /// again here, from this run's point of view.
+            void
+            Forget(TestResult &test)
+            {
+                test.quarantined = false;
+                test.history = FailureHistory::kUnknown;
+                test.selectionReason.clear();
+                test.signature.clear();
+                test.analysis.clear();
+                test.replayCommand.clear();
+                test.predictedDurationMicroseconds = 0;
+                test.predictedFailureProbability = 0.0;
+            }
+
+            Expected<TestResult>
+            ReadLine(const JsonValue &value)
+            {
+                TestResult test = TestResultFromJson(value);
+                Forget(test);
+                if (test.name.empty())
+                {
+                    test.name = test.id;
+                }
+                if (test.name.empty())
+                {
+                    return Error{ "a test needs an 'id' or a 'name'" };
+                }
+                const std::string &outcome = value["outcome"].AsString();
+                if (!OutcomeFromName(outcome))
+                {
+                    return Error{ "'" + test.name + "' has the outcome '"
+                                  + outcome + "'" };
+                }
+                if (test.attempts.empty())
+                {
+                    Attempt attempt = ImportedAttempt(
+                        test.outcome,
+                        value["durationMicroseconds"].AsInteger(),
+                        value["message"].AsString(),
+                        value["details"].AsString(),
+                        test.category);
+                    attempt.standardOutput = value["standardOutput"].AsString();
+                    attempt.standardError = value["standardError"].AsString();
+                    test.attempts.push_back(std::move(attempt));
+                }
+                return test;
+            }
+
+            Expected<std::vector<TestResult>>
+            ParseLines(std::string_view text)
+            {
+                std::vector<TestResult> tests;
+                std::size_t number = 0;
+                bool started = false;
+                for (const auto line : ImportLines(text))
+                {
+                    ++number;
+                    if (ImportTrim(line).empty())
+                    {
+                        continue;
+                    }
+                    const std::string where = "line " + std::to_string(number);
+                    auto value = ParseJson(line);
+                    if (!value)
+                    {
+                        return value.GetError().Context(where);
+                    }
+                    if (!started)
+                    {
+                        started = true;
+                        if ((*value)["format"].AsString() != "catch3-results")
+                        {
+                            return Error{ "the first line must name the format "
+                                          "catch3-results" };
+                        }
+                        if ((*value)["version"].AsInteger()
+                            > kResultsFormatVersion)
+                        {
+                            return Error{ "the format is newer than this "
+                                          "version of Catch3 reads" };
+                        }
+                        continue;
+                    }
+                    auto test = ReadLine(*value);
+                    if (!test)
+                    {
+                        return test.GetError().Context(where);
+                    }
+                    tests.push_back(std::move(*test));
+                }
+                return tests;
+            }
+
+            Expected&