db: Test truncated keys are invalid; NFC

internal/db/paste_test.go

@@ -75,3 +75,26 @@ func TestGeneratedKeysAreValid(t *testing.T) {
 		}
 	}
 }
+
+func TestTruncatedKeysAreInvalid(t *testing.T) {
+	db, err := OpenTemporaryDB()
+	if err != nil {
+		t.Error(err)
+	}
+	var minimumEntropy int
+	checkTruncatedKeysInvalid := func(truncRand uint) bool {
+		key, err := GeneratePasteKey(db, minimumEntropy)
+		if err != nil {
+			return false
+		}
+		trunc := int(truncRand % uint(len(key)-1))
+		key = key[:trunc]
+		return ValidatePasteKey(key) == ErrKeyInvalidLength
+	}
+
+	for minimumEntropy = 0; minimumEntropy <= 80; minimumEntropy++ {
+		if err = quick.Check(checkTruncatedKeysInvalid, nil); err != nil {
+			t.Error(err)
+		}
+	}
+}