Support mocking `new Date()` & `Date.now()` in bun:test (#3501)

* Support changing the time

* Bump WebKit

* Update bun.lockb

---------

Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/bun.js/bindings/JSMockFunction.cpp b/src/bun.js/bindings/JSMockFunction.cpp
index 33922c2b7..0e24e761c 100644
--- a/src/bun.js/bindings/JSMockFunction.cpp
+++ b/src/bun.js/bindings/JSMockFunction.cpp
@@ -19,6 +19,7 @@
 #include <JavaScriptCore/WeakMapImpl.h>
 #include <JavaScriptCore/WeakMapImplInlines.h>
 #include <JavaScriptCore/FunctionPrototype.h>
+#include <JavaScriptCore/DateInstance.h>
 
 namespace Bun {
 
@@ -65,6 +66,29 @@ JSC_DECLARE_HOST_FUNCTION(jsMockFunctionMockRejectedValueOnce);
 JSC_DECLARE_HOST_FUNCTION(jsMockFunctionWithImplementationCleanup);
 JSC_DECLARE_HOST_FUNCTION(jsMockFunctionWithImplementation);
 
+extern "C" EncodedJSValue JSMock__jsNow(JSC::JSGlobalObject* globalObject, JSC::CallFrame* callFrame)
+{
+    return JSValue::encode(jsNumber(globalObject->jsDateNow()));
+}
+extern "C" EncodedJSValue JSMock__jsSetSystemTime(JSC::JSGlobalObject* globalObject, JSC::CallFrame* callFrame)
+{
+    JSValue argument0 = callFrame->argument(0);
+
+    if (auto* dateInstance = jsDynamicCast<DateInstance*>(argument0)) {
+        if (std::isnormal(dateInstance->internalNumber())) {
+            globalObject->overridenDateNow = dateInstance->internalNumber();
+        }
+        return JSValue::encode(callFrame->thisValue());
+    }
+
+    if (argument0.isNumber() && argument0.asNumber() > 0) {
+        globalObject->overridenDateNow = argument0.asNumber();
+    }
+
+    globalObject->overridenDateNow = -1;
+    return JSValue::encode(callFrame->thisValue());
+}
+
 uint64_t JSMockModule::s_nextInvocationId = 0;
 
 // This is taken from JSWeakSet