diff --git a/modules/libcom/test/Makefile b/modules/libcom/test/Makefile
index 99e7e2bd52..6e5bd19a7d 100644
--- a/modules/libcom/test/Makefile
+++ b/modules/libcom/test/Makefile
@@ -209,6 +209,11 @@ aslibtest_SRCS += aslibtest.c
 testHarness_SRCS += aslibtest.c
 TESTS += aslibtest
 
+TESTPROD_HOST += fdManagerTest
+fdManagerTest_SRCS += fdManagerTest.cpp
+testHarness_SRCS += fdManagerTest.cpp
+TESTS += fdManagerTest
+
 # Perl module tests:
 TESTS += macLib
 
diff --git a/modules/libcom/test/epicsRunLibComTests.c b/modules/libcom/test/epicsRunLibComTests.c
index 54c46a68ec..d560fd46a2 100644
--- a/modules/libcom/test/epicsRunLibComTests.c
+++ b/modules/libcom/test/epicsRunLibComTests.c
@@ -54,6 +54,7 @@ int initHookTest(void);
 int ipAddrToAsciiTest(void);
 int macDefExpandTest(void);
 int macLibTest(void);
+int fdManagerTest(void);
 int osiSockTest(void);
 int ringBytesTest(void);
 int ringPointerTest(void);
@@ -110,6 +111,7 @@ void epicsRunLibComTests(void)
     runTest(ipAddrToAsciiTest);
     runTest(macDefExpandTest);
     runTest(macLibTest);
+    runTest(fdManagerTest);
     runTest(osiSockTest);
     runTest(ringBytesTest);
     runTest(ringPointerTest);
diff --git a/modules/libcom/test/fdManagerTest.cpp b/modules/libcom/test/fdManagerTest.cpp
new file mode 100644
index 0000000000..49c1e96ce5
--- /dev/null
+++ b/modules/libcom/test/fdManagerTest.cpp
@@ -0,0 +1,312 @@
+/*************************************************************************\
+* Copyright (c) 2025 Michael Davidsaver
+* SPDX-License-Identifier: EPICS
+* EPICS Base is distributed subject to a Software License Agreement found
+* in file LICENSE that is included with this distribution.
+\*************************************************************************/
+
+#include <algorithm>
+
+#include <osiSock.h>
+#include <fdManager.h>
+#include <epicsTime.h>
+#include <epicsAtomic.h>
+#include <epicsThread.h>
+
+#include <epicsUnitTest.h>
+#include <testMain.h>
+
+#if __cplusplus<201103L
+#  define final
+#  define override
+#endif
+
+namespace {
+
+void set_non_blocking(SOCKET sd)
+{
+    osiSockIoctl_t yes = true;
+    int status = socket_ioctl ( sd,
+                                FIONBIO, & yes);
+    if(status)
+        testFail("set_non_blocking fails : %d", SOCKERRNO);
+}
+
+// RAII for epicsTimer
+struct ScopedTimer {
+    epicsTimer& timer;
+    ScopedTimer(epicsTimer& t) :timer(t) {}
+    ~ScopedTimer() { timer.destroy(); }
+};
+struct ScopedFDReg {
+    fdReg * const reg;
+    ScopedFDReg(fdReg* reg) :reg(reg) {}
+    ~ScopedFDReg() { reg->destroy(); }
+};
+
+// RAII for socket
+struct Socket {
+    SOCKET sd;
+    Socket() :sd(INVALID_SOCKET) {}
+    explicit
+    Socket(SOCKET sd) :sd(sd) {}
+    Socket(int af, int type)
+        :sd(epicsSocketCreate(af, type, 0))
+    {
+        if(sd==INVALID_SOCKET)
+            testAbort("failed to allocate socket %d %d", af, type);
+    }
+private:
+    Socket(const Socket&);
+    Socket& operator=(const Socket&);
+public:
+    ~Socket() {
+        if(sd!=INVALID_SOCKET)
+            epicsSocketDestroy(sd);
+    }
+    void swap(Socket& o) {
+        std::swap(sd, o.sd);
+    }
+    sockaddr_in bind()
+    {
+        sockaddr_in addr;
+        memset(&addr, 0, sizeof(addr));
+        addr.sin_family = AF_INET;
+        addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+
+        if(::bind(sd, (sockaddr*)&addr, sizeof(addr)))
+            testAbort("Unable to bind lo : %d", SOCKERRNO);
+
+        sockaddr_in ret;
+        osiSocklen_t addrlen = sizeof(ret);
+        if(getsockname(sd, (sockaddr*)&ret, &addrlen))
+            testAbort("Unable to getsockname : %d", SOCKERRNO);
+        (void)addrlen;
+
+        if(listen(sd, 1))
+            testAbort("Unable to listen : %d", SOCKERRNO);
+
+        return ret;
+    }
+};
+
+struct DoConnect final : public epicsThreadRunable {
+    const SOCKET sd;
+    sockaddr_in to;
+    DoConnect(SOCKET sd, const sockaddr_in& to)
+        :sd(sd)
+        ,to(to)
+    {}
+
+    void run() override final {
+        int err = connect(sd, (sockaddr*)&to, sizeof(to));
+        testOk(err==0, "connect() %d %d", err, SOCKERRNO);
+    }
+};
+
+struct DoAccept final : public epicsThreadRunable {
+    const SOCKET sd;
+    Socket peer;
+    sockaddr_in peer_addr;
+    DoAccept(SOCKET sd) :sd(sd) {}
+    void run() override final {
+        osiSocklen_t len(sizeof(peer_addr));
+        Socket temp(accept(sd, (sockaddr*)&peer_addr, &len));
+        if(temp.sd==INVALID_SOCKET)
+            testFail("accept() -> %d", SOCKERRNO);
+        temp.swap(peer);
+    }
+};
+
+struct DoRead final : public epicsThreadRunable {
+    const SOCKET sd;
+    void* buf;
+    unsigned buflen;
+    int n;
+    DoRead(SOCKET sd, void* buf, unsigned buflen): sd(sd), buf(buf), buflen(buflen), n(0) {}
+    void run() override final {
+        n = recv(sd, (char*)buf, buflen, 0);
+        if(n<0)
+            testFail("read() -> %d, %d", n, SOCKERRNO);
+    }
+};
+
+struct DoWriteAll final : public epicsThreadRunable {
+    const SOCKET sd;
+    const void* buf;
+    unsigned buflen;
+    DoWriteAll(SOCKET sd, const void* buf, unsigned buflen): sd(sd), buf(buf), buflen(buflen) {}
+    void run() override final {
+        unsigned nsent = 0;
+        while(nsent<buflen) {
+            int n = send(sd, nsent+(char*)buf, buflen-nsent, 0);
+            if(n<0) {
+                testFail("send() -> %d, %d", n, SOCKERRNO);
+                break;
+            }
+            nsent += n;
+        }
+    }
+};
+
+struct Expire final : public epicsTimerNotify {
+    bool expired;
+
+    Expire() :expired(false) {}
+    virtual ~Expire() {}
+    virtual expireStatus expire(const epicsTime &) override final
+    {
+        if(!expired) {
+            expired = true;
+            testPass("expired");
+        } else {
+            testFail("re-expired?");
+        }
+        return noRestart;
+    }
+};
+
+struct Event final : public fdReg {
+    int* ready;
+
+    Event(fdManager& mgr, fdRegType evt, SOCKET sd, int* ready)
+        :fdReg(sd, evt, false, mgr)
+        ,ready(ready)
+    {}
+    virtual ~Event() {}
+
+    virtual void callBack() override final {
+        epics::atomic::set(*ready, 1);
+    }
+};
+
+struct OneShot final : public fdReg {
+    int *mask;
+
+    OneShot(fdManager& mgr, fdRegType evt, SOCKET sd, int *mask)
+        :fdReg(sd, evt, true, mgr)
+        ,mask(mask)
+    {}
+    virtual ~OneShot() {
+        epics::atomic::add(*mask, 2);
+    }
+
+    virtual void callBack() override final {
+        epics::atomic::add(*mask, 1);
+    }
+};
+
+void testEmpty()
+{
+    fdManager empty;
+    empty.process(0.1); // ca-gateway always passes 0.01
+    testPass("Did nothing");
+}
+
+void testOnlyTimer()
+{
+    fdManager mgr;
+    Expire trig, never;
+    ScopedTimer trig_timer(mgr.createTimer()),
+                never_timer(mgr.createTimer());
+    epicsTime now(epicsTime::getCurrent());
+    trig_timer.timer.start(trig, now+0.1);
+    never_timer.timer.start(never, now+9999999.0);
+    mgr.process(0.2);
+    testOk1(trig.expired);
+    testOk1(!never.expired);
+}
+
+void testSockIO()
+{
+    fdManager mgr;
+    Socket listener(AF_INET, SOCK_STREAM);
+    set_non_blocking(listener.sd);
+    sockaddr_in servAddr(listener.bind());
+
+    Socket client(AF_INET, SOCK_STREAM);
+    Socket server;
+    // listen() / connect()
+    {
+        int readable = 0;
+        Event evt(mgr, fdrRead, listener.sd, &readable);
+        DoConnect conn(client.sd, servAddr);
+        epicsThread connector(conn, "connect", 0);
+        connector.start();
+
+        mgr.process(5.0);
+
+        testOk1(readable);
+
+        DoAccept acc(listener.sd);
+        acc.run();
+        server.swap(acc.peer);
+    }
+    set_non_blocking(server.sd);
+    // writeable
+    {
+        int mask = 0;
+        new OneShot(mgr, fdrWrite, server.sd, &mask);
+
+        mgr.process(5.0);
+
+        testOk(mask==3, "OneShot event mask %x", mask);
+    }
+    // read
+    {
+        const char msg[] = "testing";
+        int readable = 0;
+        Event evt(mgr, fdrRead, server.sd, &readable);
+        DoWriteAll op(client.sd, msg, sizeof(msg)-1);
+        epicsThread writer(op, "writer", 0);
+        writer.start();
+
+        mgr.process(5.0);
+
+        testOk1(readable);
+
+        char buf[sizeof(msg)] = "";
+        DoRead(server.sd, buf, sizeof(buf)-1).run();
+        buf[sizeof(buf)-1] = '\0';
+        testOk(strcmp(msg, buf)==0, "%s == %s", msg, buf);
+    }
+    // timer while unreadable
+    {
+
+        int readable = 0;
+        Event evt(mgr, fdrRead, server.sd, &readable);
+        Expire tmo;
+        ScopedTimer timer(mgr.createTimer());
+        timer.timer.start(tmo, epicsTime::getCurrent()); // immediate
+
+        mgr.process(1.0);
+
+        testOk1(!readable);
+        testOk1(tmo.expired);
+    }
+    // notification on close()
+    {
+        int readable = 0;
+        Event evt(mgr, fdrRead, server.sd, &readable);
+
+        shutdown(client.sd, SHUT_RDWR);
+        //Socket().swap(client);
+
+        mgr.process(1.0);
+
+        testOk1(readable);
+    }
+}
+
+} // namespace
+
+MAIN(fdManagerTest)
+{
+    testPlan(13);
+    osiSockAttach();
+    testEmpty();
+    testOnlyTimer();
+    testSockIO();
+    osiSockRelease();
+    return testDone();
+}