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Deflake real-backend forwarding tests #5963

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Merged
JAORMX merged 1 commit into from
Jul 24, 2026
Merged

Deflake real-backend forwarding tests #5963

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48 changes: 28 additions & 20 deletions pkg/vmcp/server/forwarding_realbackend_integration_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,16 @@ const (
fwdLogData = "hello-from-backend"
)

// forwardingRealBackendTimeout bounds each real-backend forwarding test. These
// exercise async, server-initiated traffic relayed backend -> vMCP -> downstream
// over real in-process HTTP clients; under the full-suite parallel `-race` load
// on CI a single relay can take many seconds. The timeout is deliberately
// generous so a slow-but-working relay is not mistaken for a hang: it is the
// single deadline the tests wait against (waitNotification derives its own
// deadline from the per-test context), so a genuine hang still fails with a
// clear error rather than blocking to the `go test` global timeout. See #5962.
const forwardingRealBackendTimeout = 60 * time.Second

// startForwardingBackend starts a real in-process MCP backend whose tools drive
// server->client traffic (elicitation, sampling, progress, logging) during a
// tools/call. Returns the backend's /mcp URL.
Expand Down Expand Up @@ -202,24 +212,22 @@ func newDownstreamClient(ctx context.Context, t *testing.T, vmcpURL string, with
return dc
}

// waitNotification blocks for a forwarded notification with the given method.
func (dc *downstreamClient) waitNotification(t *testing.T, method string) mcpmcp.JSONRPCNotification {
// waitNotification blocks for a forwarded notification with the given method,
// or until ctx is done. It waits against the caller's context rather than an
// independent hardcoded timer so there is a single deadline for the test (see
// forwardingRealBackendTimeout): a fixed timer shorter than the context flaked
// under CI `-race` load — the async backend -> vMCP -> downstream relay can take
// well over a second — while a timer longer than the context would mask a hang.
func (dc *downstreamClient) waitNotification(ctx context.Context, t *testing.T, method string) mcpmcp.JSONRPCNotification {
t.Helper()
// Give the forwarded notification generous headroom: these are async,
// server-initiated messages relayed backend -> vMCP -> downstream, and under
// the full-suite parallel `-race` load on CI the round trip can take well over
// a second. The previous 5s deadline flaked (timed out) there while passing in
// milliseconds locally. Stay under the callers' 20s context so a genuine hang
// still fails cleanly rather than blocking to the context deadline.
deadline := time.After(15 * time.Second)
for {
select {
case n := <-dc.notifCh:
if n.Method == method {
return n
}
case <-deadline:
t.Fatalf("timed out waiting for %s notification", method)
case <-ctx.Done():
t.Fatalf("timed out waiting for %s notification: %v", method, ctx.Err())
}
}
}
Expand All @@ -229,7 +237,7 @@ func (dc *downstreamClient) waitNotification(t *testing.T, method string) mcpmcp
// carried back into the tool result.
func TestForwarding_Elicitation_RealBackend(t *testing.T) {
t.Parallel()
ctx, cancel := context.WithTimeout(t.Context(), 20*time.Second)
ctx, cancel := context.WithTimeout(t.Context(), forwardingRealBackendTimeout)
defer cancel()

backendURL := startForwardingBackend(t)
Expand Down Expand Up @@ -259,7 +267,7 @@ func TestForwarding_Elicitation_RealBackend(t *testing.T) {
// message carried back into the tool result.
func TestForwarding_Sampling_RealBackend(t *testing.T) {
t.Parallel()
ctx, cancel := context.WithTimeout(t.Context(), 20*time.Second)
ctx, cancel := context.WithTimeout(t.Context(), forwardingRealBackendTimeout)
defer cancel()

backendURL := startForwardingBackend(t)
Expand All @@ -282,7 +290,7 @@ func TestForwarding_Sampling_RealBackend(t *testing.T) {
// the tool result is read.
func TestForwarding_Progress_RealBackend(t *testing.T) {
t.Parallel()
ctx, cancel := context.WithTimeout(t.Context(), 20*time.Second)
ctx, cancel := context.WithTimeout(t.Context(), forwardingRealBackendTimeout)
defer cancel()

backendURL := startForwardingBackend(t)
Expand All @@ -295,7 +303,7 @@ func TestForwarding_Progress_RealBackend(t *testing.T) {
require.NoError(t, err)
require.False(t, res.IsError)

n := dc.waitNotification(t, "notifications/progress")
n := dc.waitNotification(ctx, t, "notifications/progress")
assert.Equal(t, fwdProgressToken, n.Params.AdditionalFields["progressToken"])
assert.InDelta(t, 0.5, n.Params.AdditionalFields["progress"], 1e-9)
assert.Equal(t, "halfway", n.Params.AdditionalFields["message"])
Expand All @@ -306,7 +314,7 @@ func TestForwarding_Progress_RealBackend(t *testing.T) {
// to the downstream client, which has itself set a logging level.
func TestForwarding_Logging_RealBackend(t *testing.T) {
t.Parallel()
ctx, cancel := context.WithTimeout(t.Context(), 20*time.Second)
ctx, cancel := context.WithTimeout(t.Context(), forwardingRealBackendTimeout)
defer cancel()

backendURL := startForwardingBackend(t)
Expand All @@ -323,7 +331,7 @@ func TestForwarding_Logging_RealBackend(t *testing.T) {
require.NoError(t, err)
require.False(t, res.IsError)

n := dc.waitNotification(t, "notifications/message")
n := dc.waitNotification(ctx, t, "notifications/message")
assert.Equal(t, "info", n.Params.AdditionalFields["level"])
assert.Equal(t, fwdLogData, n.Params.AdditionalFields["data"])
}
Expand All @@ -334,7 +342,7 @@ func TestForwarding_Logging_RealBackend(t *testing.T) {
// the deadline.
func TestForwarding_Sampling_NoDownstreamCapability(t *testing.T) {
t.Parallel()
ctx, cancel := context.WithTimeout(t.Context(), 20*time.Second)
ctx, cancel := context.WithTimeout(t.Context(), forwardingRealBackendTimeout)
defer cancel()

backendURL := startForwardingBackend(t)
Expand All @@ -359,7 +367,7 @@ func TestForwarding_Sampling_NoDownstreamCapability(t *testing.T) {
// cleanly (a failed tools/call) rather than hanging until the deadline.
func TestForwarding_Elicitation_NoDownstreamCapability(t *testing.T) {
t.Parallel()
ctx, cancel := context.WithTimeout(t.Context(), 20*time.Second)
ctx, cancel := context.WithTimeout(t.Context(), forwardingRealBackendTimeout)
defer cancel()

backendURL := startForwardingBackend(t)
Expand Down Expand Up @@ -442,7 +450,7 @@ func newSamplingClient(ctx context.Context, t *testing.T, vmcpURL, summary, mode
// would be lopsided (A=0, B=2 instead of 1/1) — either check trips.
func TestForwarding_Sampling_RealBackend_SessionIsolation(t *testing.T) {
t.Parallel()
ctx, cancel := context.WithTimeout(t.Context(), 30*time.Second)
ctx, cancel := context.WithTimeout(t.Context(), forwardingRealBackendTimeout)
defer cancel()

backendURL := startForwardingBackend(t)
Expand Down
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