diff --git a/src/libstore/tests/characterization.hh b/src/libstore/tests/characterization.hh
new file mode 100644
index 000000000..5f366cb42
--- /dev/null
+++ b/src/libstore/tests/characterization.hh
@@ -0,0 +1,23 @@
+#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";
+}
+
+}
diff --git a/src/libstore/tests/common-protocol.cc b/src/libstore/tests/common-protocol.cc
new file mode 100644
index 000000000..de57211f0
--- /dev/null
+++ b/src/libstore/tests/common-protocol.cc
@@ -0,0 +1,152 @@
+#include <regex>
+
+#include <nlohmann/json.hpp>
+#include <gtest/gtest.h>
+
+#include "common-protocol.hh"
+#include "common-protocol-impl.hh"
+#include "build-result.hh"
+#include "tests/protocol.hh"
+#include "tests/characterization.hh"
+
+namespace nix {
+
+const char commonProtoDir[] = "common-protocol";
+
+using CommonProtoTest = ProtoTest<CommonProto, commonProtoDir>;
+
+CHARACTERIZATION_TEST(
+    CommonProtoTest,
+    string,
+    "string",
+    (std::tuple<std::string, std::string, std::string, std::string, std::string> {
+        "",
+        "hi",
+        "white rabbit",
+        "大白兔",
+        "oh no \0\0\0 what was that!",
+    }))
+
+CHARACTERIZATION_TEST(
+    CommonProtoTest,
+    storePath,
+    "store-path",
+    (std::tuple<StorePath, StorePath> {
+        StorePath { "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo" },
+        StorePath { "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo-bar" },
+    }))
+
+CHARACTERIZATION_TEST(
+    CommonProtoTest,
+    contentAddress,
+    "content-address",
+    (std::tuple<ContentAddress, ContentAddress, ContentAddress> {
+        ContentAddress {
+            .method = TextIngestionMethod {},
+            .hash = hashString(HashType::htSHA256, "Derive(...)"),
+        },
+        ContentAddress {
+            .method = FileIngestionMethod::Flat,
+            .hash = hashString(HashType::htSHA1, "blob blob..."),
+        },
+        ContentAddress {
+            .method = FileIngestionMethod::Recursive,
+            .hash = hashString(HashType::htSHA256, "(...)"),
+        },
+    }))
+
+CHARACTERIZATION_TEST(
+    CommonProtoTest,
+    drvOutput,
+    "drv-output",
+    (std::tuple<DrvOutput, DrvOutput> {
+        {
+            .drvHash = Hash::parseSRI("sha256-FePFYIlMuycIXPZbWi7LGEiMmZSX9FMbaQenWBzm1Sc="),
+            .outputName = "baz",
+        },
+        DrvOutput {
+            .drvHash = Hash::parseSRI("sha256-b4afnqKCO9oWXgYHb9DeQ2berSwOjS27rSd9TxXDc/U="),
+            .outputName = "quux",
+        },
+    }))
+
+CHARACTERIZATION_TEST(
+    CommonProtoTest,
+    realisation,
+    "realisation",
+    (std::tuple<Realisation, Realisation> {
+        Realisation {
+            .id = DrvOutput {
+                .drvHash = Hash::parseSRI("sha256-FePFYIlMuycIXPZbWi7LGEiMmZSX9FMbaQenWBzm1Sc="),
+                .outputName = "baz",
+            },
+            .outPath = StorePath { "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo" },
+            .signatures = { "asdf", "qwer" },
+        },
+        Realisation {
+            .id = {
+                .drvHash = Hash::parseSRI("sha256-FePFYIlMuycIXPZbWi7LGEiMmZSX9FMbaQenWBzm1Sc="),
+                .outputName = "baz",
+            },
+            .outPath = StorePath { "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo" },
+            .signatures = { "asdf", "qwer" },
+            .dependentRealisations = {
+                {
+                    DrvOutput {
+                        .drvHash = Hash::parseSRI("sha256-b4afnqKCO9oWXgYHb9DeQ2berSwOjS27rSd9TxXDc/U="),
+                        .outputName = "quux",
+                    },
+                    StorePath { "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo" },
+                },
+            },
+        },
+    }))
+
+CHARACTERIZATION_TEST(
+    CommonProtoTest,
+    vector,
+    "vector",
+    (std::tuple<std::vector<std::string>, std::vector<std::string>, std::vector<std::string>, std::vector<std::vector<std::string>>> {
+        { },
+        { "" },
+        { "", "foo", "bar" },
+        { {}, { "" }, { "", "1", "2" } },
+    }))
+
+CHARACTERIZATION_TEST(
+    CommonProtoTest,
+    set,
+    "set",
+    (std::tuple<std::set<std::string>, std::set<std::string>, std::set<std::string>, std::set<std::set<std::string>>> {
+        { },
+        { "" },
+        { "", "foo", "bar" },
+        { {}, { "" }, { "", "1", "2" } },
+    }))
+
+CHARACTERIZATION_TEST(
+    CommonProtoTest,
+    optionalStorePath,
+    "optional-store-path",
+    (std::tuple<std::optional<StorePath>, std::optional<StorePath>> {
+        std::nullopt,
+        std::optional {
+            StorePath { "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-foo-bar" },
+        },
+    }))
+
+CHARACTERIZATION_TEST(
+    CommonProtoTest,
+    optionalContentAddress,
+    "optional-content-address",
+    (std::tuple<std::optional<ContentAddress>, std::optional<ContentAddress>> {
+        std::nullopt,
+        std::optional {
+            ContentAddress {
+                .method = FileIngestionMethod::Flat,
+                .hash = hashString(HashType::htSHA1, "blob blob..."),
+            },
+        },
+    }))
+
+}
diff --git a/src/libstore/tests/protocol.hh b/src/libstore/tests/protocol.hh
new file mode 100644
index 000000000..86a900757
--- /dev/null
+++ b/src/libstore/tests/protocol.hh
@@ -0,0 +1,88 @@
+#include <nlohmann/json.hpp>
+#include <gtest/gtest.h>
+
+#include "tests/libstore.hh"
+#include "tests/characterization.hh"
+
+namespace nix {
+
+template<class Proto, const char * protocolDir>
+class ProtoTest : public LibStoreTest
+{
+    /**
+     * Read this as simply `using S = Inner::Serialise;`.
+     *
+     * See `LengthPrefixedProtoHelper::S` for the same trick, and its
+     * rationale.
+     */
+    template<typename U> using S = typename Proto::template Serialise<U>;
+
+public:
+    Path unitTestData = getUnitTestData() + "/libstore/" + protocolDir;
+
+    Path goldenMaster(std::string_view testStem) {
+        return unitTestData + "/" + testStem + ".bin";
+    }
+
+    /**
+     * Golden test for `T` reading
+     */
+    template<typename T>
+    void readTest(PathView testStem, T value)
+    {
+        if (testAccept())
+        {
+            GTEST_SKIP() << "Cannot read golden master because another test is also updating it";
+        }
+        else
+        {
+            auto expected = readFile(goldenMaster(testStem));
+
+            T got = ({
+                StringSource from { expected };
+                S<T>::read(
+                    *store,
+                    typename Proto::ReadConn { .from = from });
+            });
+
+            ASSERT_EQ(got, value);
+        }
+    }
+
+    /**
+     * Golden test for `T` write
+     */
+    template<typename T>
+    void writeTest(PathView testStem, const T & value)
+    {
+        auto file = goldenMaster(testStem);
+
+        StringSink to;
+        Proto::write(
+            *store,
+            typename Proto::WriteConn { .to = to },
+            value);
+
+        if (testAccept())
+        {
+            createDirs(dirOf(file));
+            writeFile(file, to.s);
+            GTEST_SKIP() << "Updating golden master";
+        }
+        else
+        {
+            auto expected = readFile(file);
+            ASSERT_EQ(to.s, expected);
+        }
+    }
+};
+
+#define CHARACTERIZATION_TEST(FIXTURE, NAME, STEM, VALUE) \
+    TEST_F(FIXTURE, NAME ## _read) { \
+        readTest(STEM, VALUE); \
+    } \
+    TEST_F(FIXTURE, NAME ## _write) { \
+        writeTest(STEM, VALUE); \
+    }
+
+}
diff --git a/src/libstore/tests/worker-protocol.cc b/src/libstore/tests/worker-protocol.cc
index fa7cbe121..59d7ff96d 100644
--- a/src/libstore/tests/worker-protocol.cc
+++ b/src/libstore/tests/worker-protocol.cc
@@ -7,85 +7,17 @@
 #include "worker-protocol-impl.hh"
 #include "derived-path.hh"
 #include "build-result.hh"
-#include "tests/libstore.hh"
+#include "tests/protocol.hh"
+#include "tests/characterization.hh"
 
 namespace nix {
 
-class WorkerProtoTest : public LibStoreTest
-{
-public:
-    Path unitTestData = getEnv("_NIX_TEST_UNIT_DATA").value() + "/libstore/worker-protocol";
+const char workerProtoDir[] = "worker-protocol";
 
-    bool testAccept() {
-        return getEnv("_NIX_TEST_ACCEPT") == "1";
-    }
-
-    Path goldenMaster(std::string_view testStem) {
-        return unitTestData + "/" + testStem + ".bin";
-    }
-
-    /**
-     * Golden test for `T` reading
-     */
-    template<typename T>
-    void readTest(PathView testStem, T value)
-    {
-        if (testAccept())
-        {
-            GTEST_SKIP() << "Cannot read golden master because another test is also updating it";
-        }
-        else
-        {
-            auto expected = readFile(goldenMaster(testStem));
-
-            T got = ({
-                StringSource from { expected };
-                WorkerProto::Serialise<T>::read(
-                    *store,
-                    WorkerProto::ReadConn { .from = from });
-            });
-
-            ASSERT_EQ(got, value);
-        }
-    }
-
-    /**
-     * Golden test for `T` write
-     */
-    template<typename T>
-    void writeTest(PathView testStem, const T & value)
-    {
-        auto file = goldenMaster(testStem);
-
-        StringSink to;
-        WorkerProto::write(
-            *store,
-            WorkerProto::WriteConn { .to = to },
-            value);
-
-        if (testAccept())
-        {
-            createDirs(dirOf(file));
-            writeFile(file, to.s);
-            GTEST_SKIP() << "Updating golden master";
-        }
-        else
-        {
-            auto expected = readFile(file);
-            ASSERT_EQ(to.s, expected);
-        }
-    }
-};
-
-#define CHARACTERIZATION_TEST(NAME, STEM, VALUE)  \
-    TEST_F(WorkerProtoTest, NAME ## _read) {   \
-        readTest(STEM, VALUE);                 \
-    }                                          \
-    TEST_F(WorkerProtoTest, NAME ## _write) {  \
-        writeTest(STEM, VALUE);                \
-    }
+using WorkerProtoTest = ProtoTest<WorkerProto, workerProtoDir>;
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     string,
     "string",
     (std::tuple<std::string, std::string, std::string, std::string, std::string> {
@@ -97,6 +29,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     storePath,
     "store-path",
     (std::tuple<StorePath, StorePath> {
@@ -105,6 +38,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     contentAddress,
     "content-address",
     (std::tuple<ContentAddress, ContentAddress, ContentAddress> {
@@ -123,6 +57,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     derivedPath,
     "derived-path",
     (std::tuple<DerivedPath, DerivedPath> {
@@ -138,6 +73,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     drvOutput,
     "drv-output",
     (std::tuple<DrvOutput, DrvOutput> {
@@ -152,6 +88,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     realisation,
     "realisation",
     (std::tuple<Realisation, Realisation> {
@@ -183,6 +120,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     buildResult,
     "build-result",
     ({
@@ -240,6 +178,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     keyedBuildResult,
     "keyed-build-result",
     ({
@@ -275,6 +214,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     optionalTrustedFlag,
     "optional-trusted-flag",
     (std::tuple<std::optional<TrustedFlag>, std::optional<TrustedFlag>, std::optional<TrustedFlag>> {
@@ -284,6 +224,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     vector,
     "vector",
     (std::tuple<std::vector<std::string>, std::vector<std::string>, std::vector<std::string>, std::vector<std::vector<std::string>>> {
@@ -294,6 +235,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     set,
     "set",
     (std::tuple<std::set<std::string>, std::set<std::string>, std::set<std::string>, std::set<std::set<std::string>>> {
@@ -304,6 +246,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     optionalStorePath,
     "optional-store-path",
     (std::tuple<std::optional<StorePath>, std::optional<StorePath>> {
@@ -314,6 +257,7 @@ CHARACTERIZATION_TEST(
     }))
 
 CHARACTERIZATION_TEST(
+    WorkerProtoTest,
     optionalContentAddress,
     "optional-content-address",
     (std::tuple<std::optional<ContentAddress>, std::optional<ContentAddress>> {
diff --git a/unit-test-data/libstore/common-protocol/content-address.bin b/unit-test-data/libstore/common-protocol/content-address.bin
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diff --git a/unit-test-data/libstore/common-protocol/optional-content-address.bin b/unit-test-data/libstore/common-protocol/optional-content-address.bin
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diff --git a/unit-test-data/libstore/common-protocol/optional-store-path.bin b/unit-test-data/libstore/common-protocol/optional-store-path.bin
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diff --git a/unit-test-data/libstore/common-protocol/store-path.bin b/unit-test-data/libstore/common-protocol/store-path.bin
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