diff --git a/2020/day2/vhdl/run.sh b/2020/day2/vhdl/run.sh
index bef00f6..1f9cdcd 100755
--- a/2020/day2/vhdl/run.sh
+++ b/2020/day2/vhdl/run.sh
@@ -1,27 +1,8 @@
-#!/usr/bin/bash
+#!/bin/bash
 
-set -eu
-
-INPUT=$(readlink --canonicalize-existing "$1")
-MODE=${2:-}
-workdir=workdir
-GHDLFLAGS="--std=08 --workdir=$workdir"
+source "$COMMON_DIR/vhdl_run.sh"
 
 cd "$(dirname "${BASH_SOURCE[0]}")"
 
-mkdir -p workdir
-
-if [[ $MODE = "--synth" ]]; then
-	for step in 1 2; do
-		ghdl remove $GHDLFLAGS
-		ghdl synth $GHDLFLAGS -gCOUNTER_WIDTH=12 -gSTEP="$step" parser.vhd verifier.vhd top.vhd -e top > top_syn.vhd 2>/dev/null
-		ghdl analyze $GHDLFLAGS top_syn.vhd sim.vhd day2.vhdl
-		ghdl elab-run $GHDLFLAGS day2 -gSTEP="$step" --wave="$workdir/synth$step.ghw" --ieee-asserts=disable < "$INPUT"
-	done
-else
-	ghdl remove $GHDLFLAGS
-	ghdl analyze $GHDLFLAGS parser.vhd verifier.vhd top.vhd sim.vhd day2.vhd
-	for step in 1 2; do
-		ghdl elab-run $GHDLFLAGS day2 -gSTEP="$step" --wave="$workdir/sim$step.ghw" < "$INPUT"
-	done
-fi
+DUT_OUTPUT_WIDTH=12
+test_synth day2 parser.vhdl verifier.vhdl top.vhdl
diff --git a/2020/day2/vhdl/sim.vhd b/common/testbench.vhdl
similarity index 98%
rename from 2020/day2/vhdl/sim.vhd
rename to common/testbench.vhdl
index 9debdb9..afdd0b7 100644
--- a/2020/day2/vhdl/sim.vhd
+++ b/common/testbench.vhdl
@@ -6,7 +6,7 @@ use std.textio.all;
 
 entity sim is
 	generic (
-		OUTPUT_WIDTH : positive := 12;
+		OUTPUT_WIDTH : positive;
 		STEP : natural range 1 to 2
 	);
 end entity;
diff --git a/common/vhdl_run.sh b/common/vhdl_run.sh
new file mode 100755
index 0000000..c2c09ab
--- /dev/null
+++ b/common/vhdl_run.sh
@@ -0,0 +1,30 @@
+#!/usr/bin/bash
+
+set -euo pipefail
+
+INPUT=$(readlink --canonicalize-existing "$1")
+workdir=workdir
+GHDLFLAGS="--std=08 --workdir=$workdir"
+
+mkdir -p workdir
+
+test_synth() {
+	local config_name=$1; shift
+
+	for step in 1 2; do
+		ghdl remove $GHDLFLAGS
+		ghdl synth $GHDLFLAGS -gOUTPUT_WIDTH="$DUT_OUTPUT_WIDTH" -gSTEP="$step" "$@" -e top > "$workdir/top_syn.vhdl" 2>/dev/null
+		ghdl analyze $GHDLFLAGS "$workdir/top_syn.vhdl" "$COMMON_DIR/testbench.vhdl" "$config_name.vhdl"
+		ghdl elab-run $GHDLFLAGS "$config_name" -gOUTPUT_WIDTH="$DUT_OUTPUT_WIDTH" --wave="$workdir/synth$step.ghw" --ieee-asserts=disable < "$INPUT"
+	done
+}
+
+test_sim() {
+	local config_name=$1; shift
+
+	ghdl remove $GHDLFLAGS
+	ghdl analyze $GHDLFLAGS "$COMMON_DIR/testbench.vhdl" "$@" "$config_name.vhdl"
+	for step in 1 2; do
+		ghdl elab-run $GHDLFLAGS "$config_name" -gOUTPUT_WIDTH="$DUT_OUTPUT_WIDTH" -gSTEP="$step" --wave="$workdir/sim$step.ghw" < "$INPUT"
+	done
+}
diff --git a/test.sh b/test.sh
index 55ad108..6b5c8a1 100755
--- a/test.sh
+++ b/test.sh
@@ -6,6 +6,8 @@ cd "$(dirname "${BASH_SOURCE[0]}")"
 
 YEAR=2020
 
+export COMMON_DIR="$(realpath common)"
+
 run_solution() {
 	if [ -d "$solution" ]; then
 		if [ -f "$solution/Cargo.toml" ]; then