diff --git a/core/CMakeLists.txt b/core/CMakeLists.txt
index 573f555..ff12ff5 100644
--- a/core/CMakeLists.txt
+++ b/core/CMakeLists.txt
@@ -55,6 +55,7 @@ target_sources(nf7_core_test
     uv/file_test.cc
     uv/parallelism_test.cc
     clock_test.cc
+    env_test.hh
     meta_env_test.cc
 )
 target_link_libraries(nf7_core_test
diff --git a/iface/env_test.hh b/core/env_test.hh
similarity index 93%
rename from iface/env_test.hh
rename to core/env_test.hh
index 6eaddd3..50e10ec 100644
--- a/iface/env_test.hh
+++ b/core/env_test.hh
@@ -18,8 +18,10 @@
 #include "iface/subsys/concurrency.hh"
 #include "iface/subsys/parallelism.hh"
 
+#include "core/clock.hh"
 
-namespace nf7::test {
+
+namespace nf7::core::test {
 
 class EnvFixture : public ::testing::Test {
  public:
@@ -93,7 +95,7 @@ class EnvFixtureWithTasking : public EnvFixture {
     explicit SyncDriver(EnvFixtureWithTasking& parent) noexcept
         : parent_(parent) { }
 
-    void BeginBusy() noexcept { }
+    void BeginBusy() noexcept { parent_.clock_->Tick(); }
     void EndBusy() noexcept { }
     void Drive(SyncTask&& task) noexcept {
       try {
@@ -106,8 +108,7 @@ class EnvFixtureWithTasking : public EnvFixture {
       }
     }
     SyncTask::Time tick() const noexcept {
-      const auto now = std::chrono::system_clock::now();
-      return std::chrono::time_point_cast<SyncTask::Time::duration>(now);
+      return parent_.clock_->now();
     }
     bool nextIdleInterruption() const noexcept {
       return 0 == parent_.sq_->size();
@@ -122,9 +123,11 @@ class EnvFixtureWithTasking : public EnvFixture {
  public:
   explicit EnvFixtureWithTasking(SimpleEnv::FactoryMap&& fmap = {})
       : EnvFixture(std::move(fmap)),
+        clock_(std::make_shared<Clock>()),
         sq_(std::make_shared<SimpleTaskQueue<SyncTask>>()),
         aq_(std::make_shared<SimpleTaskQueue<AsyncTask>>()),
         ad_(*this) {
+    Install<subsys::Clock>(clock_);
     Install<subsys::Concurrency>(
         std::make_shared<WrappedTaskQueue<subsys::Concurrency>>(sq_));
     Install<subsys::Parallelism>(
@@ -166,6 +169,7 @@ class EnvFixtureWithTasking : public EnvFixture {
   }
 
  private:
+  std::shared_ptr<Clock> clock_;
   std::shared_ptr<SimpleTaskQueue<SyncTask>>  sq_;
   std::shared_ptr<SimpleTaskQueue<AsyncTask>> aq_;
 
@@ -174,4 +178,4 @@ class EnvFixtureWithTasking : public EnvFixture {
   AsyncDriver ad_;
 };
 
-}  // namespace nf7::test
+}  // namespace nf7::core::test
diff --git a/core/gl3/context_test.cc b/core/gl3/context_test.cc
index dcdff7b..b1b9ebf 100644
--- a/core/gl3/context_test.cc
+++ b/core/gl3/context_test.cc
@@ -7,13 +7,13 @@
 
 #include "iface/subsys/concurrency.hh"
 
-#include "iface/env_test.hh"
+#include "core/env_test.hh"
 
 
 using namespace std::literals;
 
 
-class Gl3Context : public nf7::test::EnvFixtureWithTasking {
+class Gl3Context : public nf7::core::test::EnvFixtureWithTasking {
  public:
   Gl3Context() noexcept : skip_(nullptr == std::getenv("NF7_TEST_GL3")) { }
 
@@ -22,12 +22,12 @@ class Gl3Context : public nf7::test::EnvFixtureWithTasking {
     if (skip_) {
       GTEST_SKIP();
     } else {
-      nf7::test::EnvFixtureWithTasking::SetUp();
+      nf7::core::test::EnvFixtureWithTasking::SetUp();
     }
   }
   void TearDown() override {
     if (!skip_) {
-      nf7::test::EnvFixtureWithTasking::TearDown();
+      nf7::core::test::EnvFixtureWithTasking::TearDown();
     }
   }
 
diff --git a/core/luajit/context_test.hh b/core/luajit/context_test.hh
index 946067c..b917747 100644
--- a/core/luajit/context_test.hh
+++ b/core/luajit/context_test.hh
@@ -18,12 +18,12 @@
 #include "iface/subsys/parallelism.hh"
 #include "iface/env.hh"
 
-#include "iface/env_test.hh"
+#include "core/env_test.hh"
 
 namespace nf7::core::luajit::test {
 
 class ContextFixture :
-    public nf7::test::EnvFixtureWithTasking,
+    public nf7::core::test::EnvFixtureWithTasking,
     public ::testing::WithParamInterface<Context::Kind> {
  public:
   ContextFixture() noexcept
diff --git a/core/luajit/lambda_test.cc b/core/luajit/lambda_test.cc
index a5e81a7..1f5b78b 100644
--- a/core/luajit/lambda_test.cc
+++ b/core/luajit/lambda_test.cc
@@ -173,13 +173,6 @@ TEST_P(LuaJIT_Lambda, CtxSleep) {
   EXPECT_GE(end-begin, 100ms);
 }
 
-TEST_P(LuaJIT_Lambda, CtxSleepWithoutClock) {
-  Expect(
-      "local ctx = ...\nctx:sleep(100)",
-      {nf7::Value {}},
-      0, 1);
-}
-
 TEST_P(LuaJIT_Lambda, CtxLogging) {
   const auto logger = std::make_shared<nf7::subsys::test::LoggerMock>();
 
diff --git a/core/sqlite/database_test.hh b/core/sqlite/database_test.hh
index 0abe8e6..d306a0a 100644
--- a/core/sqlite/database_test.hh
+++ b/core/sqlite/database_test.hh
@@ -8,15 +8,15 @@
 #include <chrono>
 #include <memory>
 
-#include "iface/env_test.hh"
+#include "core/env_test.hh"
 
 
 namespace nf7::core::sqlite::test {
 
-class DatabaseFixture : public nf7::test::EnvFixtureWithTasking {
+class DatabaseFixture : public nf7::core::test::EnvFixtureWithTasking {
  public:
   DatabaseFixture()
-      : nf7::test::EnvFixtureWithTasking({
+      : nf7::core::test::EnvFixtureWithTasking({
               {typeid(nf7::subsys::Database), [](auto& env) {
                 return std::make_shared<Database>(env, ":memory:");
               }},
diff --git a/core/uv/context_test.hh b/core/uv/context_test.hh
index 41a5b37..d4f5160 100644
--- a/core/uv/context_test.hh
+++ b/core/uv/context_test.hh
@@ -13,15 +13,15 @@
 
 #include "core/uv/clock.hh"
 
-#include "iface/env_test.hh"
+#include "core/env_test.hh"
 
 
 namespace nf7::core::uv::test {
 
-class ContextFixture : public nf7::test::EnvFixture {
+class ContextFixture : public nf7::core::test::EnvFixture {
  public:
   ContextFixture() noexcept
-      : nf7::test::EnvFixture({
+      : nf7::core::test::EnvFixture({
             SimpleEnv::MakePair<Context, MainContext>(),
             SimpleEnv::MakePair<subsys::Clock, Clock>(),
           }) {
@@ -29,12 +29,12 @@ class ContextFixture : public nf7::test::EnvFixture {
 
  protected:
   void SetUp() override {
-    nf7::test::EnvFixture::SetUp();
+    nf7::core::test::EnvFixture::SetUp();
     ctx_ = std::dynamic_pointer_cast<MainContext>(env().Get<Context>());
   }
   void TearDown() override {
     ctx_->RunAndClose();
-    nf7::test::EnvFixture::TearDown();
+    nf7::core::test::EnvFixture::TearDown();
     ctx_ = nullptr;
   }
 
diff --git a/iface/CMakeLists.txt b/iface/CMakeLists.txt
index 03c0954..b3705d2 100644
--- a/iface/CMakeLists.txt
+++ b/iface/CMakeLists.txt
@@ -48,7 +48,6 @@ target_sources(nf7_iface_test
     common/task_test.hh
     common/value_test.cc
     subsys/logger_test.hh
-    env_test.hh
 )
 target_link_libraries(nf7_iface_test
   PRIVATE