import the revisions to the characterization test framework from cppnix

This has some Flaws for sure (like, it is going to be a bit stretched to
use for repl characterization), but it is a start.

Change-Id: I258c8beb3aee236f45818a03be83bcda858120c9

tests/unit/libstore/characterization.hh

@@ -1,28 +0,0 @@
-#pragma once
-///@file
-
-namespace nix {
-
-/**
- * The path to the `unit-test-data` directory. See the contributing
- * guide in the manual for further details.
- */
-static Path getUnitTestData() {
-    return getEnv("_NIX_TEST_UNIT_DATA").value();
-}
-
-/**
- * Whether we should update "golden masters" instead of running tests
- * against them. See the contributing guide in the manual for further
- * details.
- */
-static bool testAccept() {
-    return getEnv("_NIX_TEST_ACCEPT") == "1";
-}
-
-constexpr std::string_view cannotReadGoldenMaster =
-    "Cannot read golden master because another test is also updating it";
-
-constexpr std::string_view updatingGoldenMaster =
-    "Updating golden master";
-}

tests/unit/libstore/common-protocol.cc

@@ -7,7 +7,7 @@
 #include "common-protocol-impl.hh"
 #include "build-result.hh"
 #include "protocol.hh"
-#include "characterization.hh"
+#include "tests/characterization.hh"
 
 namespace nix {
 

tests/unit/libstore/derivation.cc

@@ -5,7 +5,7 @@
 #include "derivations.hh"
 
 #include "tests/libstore.hh"
-#include "characterization.hh"
+#include "tests/characterization.hh"
 
 namespace nix {
 

tests/unit/libstore/protocol.hh

@@ -2,7 +2,7 @@
 #include <gtest/gtest.h>
 
 #include "tests/libstore.hh"
-#include "characterization.hh"
+#include "tests/characterization.hh"
 
 namespace nix {
 

tests/unit/libstore/serve-protocol.cc

@@ -7,7 +7,7 @@
 #include "serve-protocol-impl.hh"
 #include "build-result.hh"
 #include "protocol.hh"
-#include "characterization.hh"
+#include "tests/characterization.hh"
 
 namespace nix {
 

tests/unit/libstore/worker-protocol.cc

@@ -8,7 +8,7 @@
 #include "derived-path.hh"
 #include "build-result.hh"
 #include "protocol.hh"
-#include "characterization.hh"
+#include "tests/characterization.hh"
 
 namespace nix {
 

tests/unit/libutil-support/tests/characterization.hh

@@ -0,0 +1,116 @@
+#pragma once
+///@file
+
+#include <gtest/gtest.h>
+
+#include <filesystem>
+
+#include "util.hh"
+#include "types.hh"
+
+namespace nix {
+
+/**
+ * The path to the unit test data directory. See the contributing guide
+ * in the manual for further details.
+ */
+static Path getUnitTestData() {
+    return getEnv("_NIX_TEST_UNIT_DATA").value();
+}
+
+/**
+ * Whether we should update "golden masters" instead of running tests
+ * against them. See the contributing guide in the manual for further
+ * details.
+ */
+static bool testAccept() {
+    return getEnv("_NIX_TEST_ACCEPT") == "1";
+}
+
+/**
+ * Mixin class for writing characterization tests
+ */
+class CharacterizationTest : public virtual ::testing::Test
+{
+protected:
+    /**
+     * While the "golden master" for this characterization test is
+     * located. It should not be shared with any other test.
+     */
+    virtual Path goldenMaster(PathView testStem) const = 0;
+
+public:
+    /**
+     * Golden test for reading
+     *
+     * @param test hook that takes the contents of the file and does the
+     * actual work
+     */
+    void readTest(PathView testStem, auto && test)
+    {
+        auto file = goldenMaster(testStem);
+
+        if (testAccept())
+        {
+            GTEST_SKIP()
+                << "Cannot read golden master "
+                << file
+                << "because another test is also updating it";
+        }
+        else
+        {
+            test(readFile(file));
+        }
+    }
+
+    /**
+     * Golden test for writing
+     *
+     * @param test hook that produces contents of the file and does the
+     * actual work
+     */
+    void writeTest(
+        PathView testStem, auto && test, auto && readFile2, auto && writeFile2)
+    {
+        auto file = goldenMaster(testStem);
+
+        auto got = test();
+
+        if (testAccept())
+        {
+            createDirs(dirOf(file));
+            writeFile2(file, got);
+            GTEST_SKIP()
+                << "Updating golden master "
+                << file;
+        }
+        else
+        {
+            decltype(got) expected = readFile2(file);
+            ASSERT_EQ(got, expected);
+        }
+    }
+
+    /**
+     * Specialize to `std::string`
+     */
+    void writeTest(PathView testStem, auto && test)
+    {
+        writeTest(
+            testStem, test,
+            [](const Path & f) -> std::string {
+                return readFile(f);
+            },
+            [](const Path & f, const std::string & c) {
+                return writeFile(f, c);
+            });
+    }
+};
+
+constexpr std::string_view cannotReadGoldenMaster =
+    "Cannot read golden master because another test is also updating it";
+
+constexpr std::string_view updatingGoldenMaster =
+    "Updating golden master";
+
+}