diff --git a/src/libstore/tests/nar-info-disk-cache.cc b/src/libstore/tests/nar-info-disk-cache.cc
index 0597fdc41..b4bdb8329 100644
--- a/src/libstore/tests/nar-info-disk-cache.cc
+++ b/src/libstore/tests/nar-info-disk-cache.cc
@@ -9,96 +9,115 @@
 namespace nix {
 
 TEST(NarInfoDiskCacheImpl, create_and_read) {
+    // This is a large single test to avoid some setup overhead.
+
     int prio = 12345;
     bool wantMassQuery = true;
 
     Path tmpDir = createTempDir();
     AutoDelete delTmpDir(tmpDir);
     Path dbPath(tmpDir + "/test-narinfo-disk-cache.sqlite");
-    auto cache = getTestNarInfoDiskCache(dbPath);
 
-    {
-        auto bc1 = cache->createCache("https://bar", "/nix/storedir", wantMassQuery, prio);
-        auto bc2 = cache->createCache("https://xyz", "/nix/storedir", false, 12);
-        ASSERT_NE(bc1, bc2);
-    }
-
-    int savedId = cache->createCache("http://foo", "/nix/storedir", wantMassQuery, prio);;
-    {
-        auto r = cache->upToDateCacheExists("http://foo");
-        ASSERT_TRUE(r);
-        ASSERT_EQ(r->priority, prio);
-        ASSERT_EQ(r->wantMassQuery, wantMassQuery);
-        ASSERT_EQ(savedId, r->id);
-    }
-
-    SQLite db(dbPath);
+    int savedId;
+    int barId;
+    SQLite db;
     SQLiteStmt getIds;
-    getIds.create(db, "SELECT id FROM BinaryCaches WHERE url = 'http://foo'");
 
     {
-        auto q(getIds.use());
-        ASSERT_TRUE(q.next());
-        ASSERT_EQ(savedId, q.getInt(0));
-        ASSERT_FALSE(q.next());
-    }
+        auto cache = getTestNarInfoDiskCache(dbPath);
 
-    db.exec("UPDATE BinaryCaches SET timestamp = timestamp - 1 - 7 * 24 * 3600;");
+        // Set up "background noise" and check that different caches receive different ids
+        {
+            auto bc1 = cache->createCache("https://bar", "/nix/storedir", wantMassQuery, prio);
+            auto bc2 = cache->createCache("https://xyz", "/nix/storedir", false, 12);
+            ASSERT_NE(bc1, bc2);
+            barId = bc1;
+        }
 
-    // Relies on memory cache
-    {
-        auto r = cache->upToDateCacheExists("http://foo");
-        ASSERT_TRUE(r);
-        ASSERT_EQ(r->priority, prio);
-        ASSERT_EQ(r->wantMassQuery, wantMassQuery);
-    }
+        // Check that the fields are saved and returned correctly. This does not test
+        // the select statement yet, because of in-memory caching.
+        savedId = cache->createCache("http://foo", "/nix/storedir", wantMassQuery, prio);;
+        {
+            auto r = cache->upToDateCacheExists("http://foo");
+            ASSERT_TRUE(r);
+            ASSERT_EQ(r->priority, prio);
+            ASSERT_EQ(r->wantMassQuery, wantMassQuery);
+            ASSERT_EQ(savedId, r->id);
+        }
 
-    // We can't clear the in-memory cache, so we use a new cache object.
-    auto cache2 = getTestNarInfoDiskCache(dbPath);
+        // We're going to pay special attention to the id field because we had a bug
+        // that changed it.
+        db = SQLite(dbPath);
+        getIds.create(db, "select id from BinaryCaches where url = 'http://foo'");
 
-    {
-        auto r = cache2->upToDateCacheExists("http://foo");
-        ASSERT_FALSE(r);
-    }
+        {
+            auto q(getIds.use());
+            ASSERT_TRUE(q.next());
+            ASSERT_EQ(savedId, q.getInt(0));
+            ASSERT_FALSE(q.next());
+        }
 
-    // Update, same data, check that the id number is reused
-    cache2->createCache("http://foo", "/nix/storedir", wantMassQuery, prio);
+        // Pretend that the caches are older, but keep one up to date, as "background noise"
+        db.exec("update BinaryCaches set timestamp = timestamp - 1 - 7 * 24 * 3600 where url <> 'https://xyz';");
 
-    {
-        auto r = cache2->upToDateCacheExists("http://foo");
-        ASSERT_TRUE(r);
-        ASSERT_EQ(r->priority, prio);
-        ASSERT_EQ(r->wantMassQuery, wantMassQuery);
-        ASSERT_EQ(r->id, savedId);
+        // This shows that the in-memory cache works
+        {
+            auto r = cache->upToDateCacheExists("http://foo");
+            ASSERT_TRUE(r);
+            ASSERT_EQ(r->priority, prio);
+            ASSERT_EQ(r->wantMassQuery, wantMassQuery);
+        }
     }
 
     {
-        auto q(getIds.use());
-        ASSERT_TRUE(q.next());
-        auto currentId = q.getInt(0);
-        ASSERT_FALSE(q.next());
-        ASSERT_EQ(currentId, savedId);
+        // We can't clear the in-memory cache, so we use a new cache object. This is
+        // more realistic anyway.
+        auto cache2 = getTestNarInfoDiskCache(dbPath);
+
+        {
+            auto r = cache2->upToDateCacheExists("http://foo");
+            ASSERT_FALSE(r);
+        }
+
+        // "Update", same data, check that the id number is reused
+        cache2->createCache("http://foo", "/nix/storedir", wantMassQuery, prio);
+
+        {
+            auto r = cache2->upToDateCacheExists("http://foo");
+            ASSERT_TRUE(r);
+            ASSERT_EQ(r->priority, prio);
+            ASSERT_EQ(r->wantMassQuery, wantMassQuery);
+            ASSERT_EQ(r->id, savedId);
+        }
+
+        {
+            auto q(getIds.use());
+            ASSERT_TRUE(q.next());
+            auto currentId = q.getInt(0);
+            ASSERT_FALSE(q.next());
+            ASSERT_EQ(currentId, savedId);
+        }
+
+        // Check that the fields can be modified, and the id remains the same
+        {
+            auto r0 = cache2->upToDateCacheExists("https://bar");
+            ASSERT_FALSE(r0);
+
+            cache2->createCache("https://bar", "/nix/storedir", !wantMassQuery, prio + 10);
+            auto r = cache2->upToDateCacheExists("https://bar");
+            ASSERT_EQ(r->wantMassQuery, !wantMassQuery);
+            ASSERT_EQ(r->priority, prio + 10);
+            ASSERT_EQ(r->id, barId);
+        }
+
+        // // Force update (no use case yet; we only retrieve cache metadata when stale based on timestamp)
+        // {
+        //     cache2->createCache("https://bar", "/nix/storedir", wantMassQuery, prio + 20);
+        //     auto r = cache2->upToDateCacheExists("https://bar");
+        //     ASSERT_EQ(r->wantMassQuery, wantMassQuery);
+        //     ASSERT_EQ(r->priority, prio + 20);
+        // }
     }
-
-    // Check that the fields can be modified
-    {
-        auto r0 = cache2->upToDateCacheExists("https://bar");
-        ASSERT_FALSE(r0);
-
-        cache2->createCache("https://bar", "/nix/storedir", !wantMassQuery, prio + 10);
-        auto r = cache2->upToDateCacheExists("https://bar");
-        ASSERT_EQ(r->wantMassQuery, !wantMassQuery);
-        ASSERT_EQ(r->priority, prio + 10);
-    }
-
-    // // Force update (no use case yet; we only retrieve cache metadata when stale based on timestamp)
-    // {
-    //     cache2->createCache("https://bar", "/nix/storedir", wantMassQuery, prio + 20);
-    //     auto r = cache2->upToDateCacheExists("https://bar");
-    //     ASSERT_EQ(r->wantMassQuery, wantMassQuery);
-    //     ASSERT_EQ(r->priority, prio + 20);
-    // }
-
 }
 
 }