1 files changed, 81 insertions, 0 deletions
diff --git a/gopls/internal/lsp/debounce_test.go b/gopls/internal/lsp/debounce_test.go
new file mode 100644
index 000000000..b5597faf5
--- /dev/null
+++ b/gopls/internal/lsp/debounce_test.go
@@ -0,0 +1,81 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package lsp
+
+import (
+	"testing"
+	"time"
+)
+
+func TestDebouncer(t *testing.T) {
+	t.Parallel()
+
+	type event struct {
+		key       string
+		order     uint64
+		wantFired bool
+	}
+	tests := []struct {
+		label  string
+		events []*event
+	}{
+		{
+			label: "overridden",
+			events: []*event{
+				{key: "a", order: 1, wantFired: false},
+				{key: "a", order: 2, wantFired: true},
+			},
+		},
+		{
+			label: "distinct labels",
+			events: []*event{
+				{key: "a", order: 1, wantFired: true},
+				{key: "b", order: 2, wantFired: true},
+			},
+		},
+		{
+			label: "reverse order",
+			events: []*event{
+				{key: "a", order: 2, wantFired: true},
+				{key: "a", order: 1, wantFired: false},
+			},
+		},
+		{
+			label: "multiple overrides",
+			events: []*event{
+				{key: "a", order: 1, wantFired: false},
+				{key: "a", order: 2, wantFired: false},
+				{key: "a", order: 3, wantFired: false},
+				{key: "a", order: 4, wantFired: false},
+				{key: "a", order: 5, wantFired: true},
+			},
+		},
+	}
+	for _, test := range tests {
+		test := test
+		t.Run(test.label, func(t *testing.T) {
+			d := newDebouncer()
+
+			delays := make([]chan time.Time, len(test.events))
+			okcs := make([]<-chan bool, len(test.events))
+
+			// Register the events in deterministic order, synchronously.
+			for i, e := range test.events {
+				delays[i] = make(chan time.Time, 1)
+				okcs[i] = d.debounce(e.key, e.order, delays[i])
+			}
+
+			// Now see which event fired.
+			for i, okc := range okcs {
+				event := test.events[i]
+				delays[i] <- time.Now()
+				fired := <-okc
+				if fired != event.wantFired {
+					t.Errorf("[key: %q, order: %d]: fired = %t, want %t", event.key, event.order, fired, event.wantFired)
+				}
+			}
+		})
+	}
+}