refactor-for-testability (#3)

Co-authored-by: jdl <jdl@desktop>
Co-authored-by: jdl <jdl@crumpington.com>
Reviewed-on: #3

peer/dupcheck_test.go

@@ -0,0 +1,57 @@
+package peer
+
+import (
+	"testing"
+)
+
+func TestDupCheck(t *testing.T) {
+	dc := newDupCheck(0)
+
+	for i := range bitSetSize {
+		if dc.IsDup(uint64(i)) {
+			t.Fatal("!")
+		}
+	}
+
+	type TestCase struct {
+		Counter uint64
+		Dup     bool
+	}
+
+	testCases := []TestCase{
+		{511, true},
+		{0, true},
+		{1, true},
+		{2, true},
+		{3, true},
+		{63, true},
+		{256, true},
+		{510, true},
+		{511, true},
+		{512, false},
+		{0, true},
+		{512, true},
+		{513, false},
+		{517, false},
+		{512, true},
+		{513, true},
+		{514, false},
+		{515, false},
+		{516, false},
+		{517, true},
+		{2512, false},
+		{2512, true},
+		{2001, true},
+		{2002, false},
+		{2002, true},
+		{4000, false},
+		{4000 - 511, true},  // Too old.
+		{4000 - 510, false}, // Just in the window.
+	}
+
+	for i, tc := range testCases {
+		if ok := dc.IsDup(tc.Counter); ok != tc.Dup {
+			t.Fatal(i, ok, tc)
+		}
+	}
+}