diff --git a/src/bh_assert.sv b/lib/bh_assert.sv
similarity index 96%
rename from src/bh_assert.sv
rename to lib/bh_assert.sv
index 6bdf93b..ea9f0eb 100644
--- a/src/bh_assert.sv
+++ b/lib/bh_assert.sv
@@ -1,3 +1,6 @@
+`timescale 1ns/1ps
+
+package bh_assert;
 
 int bh_assert_pass_count = 0;
 int bh_assert_fail_count = 0;
@@ -46,3 +49,4 @@ function void bh_info(string description);
     end
 endfunction
 
+endpackage
\ No newline at end of file
diff --git a/tests/common/skidbuffer.sv b/lib/skidbuffer.sv
similarity index 87%
rename from tests/common/skidbuffer.sv
rename to lib/skidbuffer.sv
index f1cf0ac..93c513b 100644
--- a/tests/common/skidbuffer.sv
+++ b/lib/skidbuffer.sv
@@ -26,14 +26,13 @@ always_ff @(posedge clk) begin
         end
 
         if (buffer_filled) begin
-            if (out_ready && !(in_valid && in_ready)) begin
+            if ((out_valid && out_ready) && !(in_valid && in_ready)) begin
                 // out_valid = 1 since buffer is full
                 buffer_filled <= 0;
             end
         end else begin
-            if (in_valid && !(out_valid && out_ready)) begin
+            if ((in_valid && in_ready) && !(out_valid && out_ready)) begin
                 // in_ready = 1 since buffer is empty
-                buffer_val = in;
                 buffer_filled <= 1;
             end
         end
diff --git a/lib/tb/.gitignore b/lib/tb/.gitignore
new file mode 100644
index 0000000..672d6da
--- /dev/null
+++ b/lib/tb/.gitignore
@@ -0,0 +1,3 @@
+*.log
+*.gtkw
+*.vcd
\ No newline at end of file
diff --git a/lib/tb/Makefile b/lib/tb/Makefile
new file mode 100644
index 0000000..349db6d
--- /dev/null
+++ b/lib/tb/Makefile
@@ -0,0 +1,23 @@
+all: verify
+
+TESTBENCH_V = $(wildcard *_tb.sv)
+SOURCE_V = $(wildcard ../*.v ../*.sv)
+LOGS = $(TESTBENCH_V:.sv=.log)
+
+# Hardware compilation
+%.out: %.sv $(SOURCE_V)
+	iverilog -g2012 -o $@ $^
+
+# Run test
+%.vcd %.log: %.out
+	./$< | tee $(patsubst %.out, %.log, $<)
+
+verify: $(LOGS)
+	@! grep -q "ERROR" $^
+	@grep -q "SUCCESS" $^
+
+clean:
+	rm -rf *.vcd *.log *.out
+
+.SECONDARY: %.log %.vcd
+.PHONY: all clean verify
diff --git a/lib/tb/skidbuffer_tb.sv b/lib/tb/skidbuffer_tb.sv
new file mode 100644
index 0000000..7da7a0d
--- /dev/null
+++ b/lib/tb/skidbuffer_tb.sv
@@ -0,0 +1,147 @@
+`timescale 1ns/1ps
+
+// import bh_assert::*;
+
+module skidbuffer_tb();
+
+int bh_assert_pass_count = 0;
+int bh_assert_fail_count = 0;
+int bh_assert_warn_count = 0;
+
+localparam BH_ASSERT_LOG_LEVEL_FAIL = 0;
+localparam BH_ASSERT_LOG_LEVEL_ASSERT = 1;
+localparam BH_ASSERT_LOG_LEVEL_WARN = 2;
+localparam BH_ASSERT_LOG_LEVEL_INFO = 3;
+
+logic bh_assert_log_level = BH_ASSERT_LOG_LEVEL_WARN;  // 0 = errors only, 1 = all assertions, 2 = warnings, 3 = info
+
+localparam COLOR_RED = "\033[31m";
+localparam COLOR_YELLOW = "\033[33m";
+localparam COLOR_GREEN = "\033[32m";
+localparam COLOR_NORMAL = "\033[0;39m";
+
+task bh_assert_equal(int val, int expected, string description);
+    // display results
+    $timeformat(-9, 2, " ns", 20);
+    $display(
+        "%t: %s: %d %s %d - %s",
+        $time,
+        val == expected ? {COLOR_GREEN, "PASS", COLOR_NORMAL} : {COLOR_RED, "FAIL", COLOR_NORMAL},
+        val,
+        val == expected ? "==" : "!=",
+        expected,
+        description
+    );
+
+    // update statistics
+    if (val == expected) begin
+        bh_assert_pass_count = bh_assert_pass_count + 1;
+    end else begin
+        bh_assert_fail_count = bh_assert_fail_count + 1;
+    end
+endtask
+
+task bh_assert_stats;
+    $timeformat(-9, 2, " ns", 20);
+    $display("%t: DONE: %1d pass, %1d fail, %1d warn", $time, bh_assert_pass_count, bh_assert_fail_count, bh_assert_warn_count);
+    if (bh_assert_pass_count + bh_assert_fail_count == 0) begin
+        $display("%sERROR%s: no assertions found", COLOR_YELLOW, COLOR_NORMAL);
+        // TODO: error in a better way?
+    end else if (bh_assert_fail_count > 0) begin
+        $display("%sERROR%s: some tests failed", COLOR_RED, COLOR_NORMAL);
+    end else begin
+        $display("%sSUCCESS%s: all tests passed", COLOR_GREEN, COLOR_NORMAL);
+    end
+endtask
+
+task bh_info(string description);
+    if (bh_assert_log_level >= BH_ASSERT_LOG_LEVEL_INFO) begin
+        $display("%t: INFO: %s", $time, description);
+    end
+endtask
+
+task bh_warn(string description);
+    if (bh_assert_log_level >= BH_ASSERT_LOG_LEVEL_WARN) begin
+        $display("%t: %sWARN%s: %s", $time, COLOR_YELLOW, COLOR_NORMAL, description);
+    end
+    bh_assert_warn_count = bh_assert_warn_count + 1;
+endtask
+
+
+parameter WIDTH = 15;
+parameter TEST_LIST_LENGTH = 256;
+
+logic clk = 0;
+logic reset = 1;
+logic [WIDTH-1:0] in;
+logic in_valid = 0;
+wire in_ready;
+wire [WIDTH-1:0] out;
+wire out_valid;
+logic out_ready = 0;
+
+skidbuffer #(
+    .WIDTH(WIDTH)
+) dut (
+    .clk(clk),
+    .reset(reset),
+    .in(in),
+    .in_valid(in_valid),
+    .in_ready(in_ready),
+    .out(out),
+    .out_valid(out_valid),
+    .out_ready(out_ready)
+);
+
+integer i = 0;
+integer in_count = 0;
+integer out_count = 0;
+logic [WIDTH-1:0] in_list [0:TEST_LIST_LENGTH-1];
+
+assign in = in_list[in_count];
+
+always #5 clk = !clk;
+
+initial begin
+    $dumpfile("skidbuffer_tb.vcd");
+    $dumpvars(0, skidbuffer_tb);
+
+    for (i=0; i<TEST_LIST_LENGTH; i=i+1) begin
+        in_list[i] = $urandom();
+    end
+
+    #10
+    reset = 0;
+
+    while (out_count < TEST_LIST_LENGTH) begin
+        #10
+        if (!in_valid || (in_valid && in_ready)) begin
+            in_valid = $urandom_range(1);
+        end
+        if (!out_ready || (out_ready && out_valid)) begin
+            out_ready = $urandom_range(1);
+        end
+    end
+
+    bh_assert_stats();
+    $finish;
+end
+
+always @(posedge clk) begin
+    if (reset == 0 && in_valid && in_ready) begin
+        in_count <= in_count + 1;
+    end
+
+    if (reset == 0 && out_valid && out_ready) begin
+        bh_assert_equal(out, in_list[out_count], $sformatf("Output value [%3d]", out_count));
+        bh_warn("hello warning");
+        bh_info("hello info");
+        out_count <= out_count + 1;
+    end
+end
+
+wire [WIDTH-1:0] out_correct;
+assign out_correct = in_list[out_count];
+
+
+endmodule
\ No newline at end of file
diff --git a/tests/common/axi4_lite.sv b/tests/common/axi4_lite.sv
index c8230ae..6835bde 100644
--- a/tests/common/axi4_lite.sv
+++ b/tests/common/axi4_lite.sv
@@ -111,6 +111,7 @@ always_ff @(posedge clk) begin
             ((axil_wvalid && axil_wready) || wdata_valid) &&
             ((axil_awvalid && axil_awready) || waddr_valid) &&
             !w_complete
+            // TODO: check for wdata_legal (and combinatorial wdata_legal)
         ) begin
             if (state_wb == STATE_IDLE) begin
                 state_wb <= STATE_WRITE;
diff --git a/tests/test_basic/Makefile b/tests/test_basic/Makefile
index 015e3ad..f9ebf04 100644
--- a/tests/test_basic/Makefile
+++ b/tests/test_basic/Makefile
@@ -2,7 +2,8 @@ all: verify
 
 TESTBENCH_V = $(wildcard *tb.sv)
 SOURCE_V = $(wildcard ../../src/*.v ../../src/*.sv)
-SOURCE_V += $(wildcard ../common/*.v) $(wildcard ../common/*.sv)
+SOURCE_V += $(wildcard ../../lib/*.v ../../lib/*.sv)
+SOURCE_V += $(wildcard ../common/*.v ../common/*.sv)
 LOGS = $(TESTBENCH_V:.sv=.log)
 
 SOURCE_C = $(wildcard *.c)
@@ -51,10 +52,8 @@ LDFLAGS = -melf32lriscv_ilp32
 	./$< | tee $(patsubst %.out, %.log, $<)
 
 verify: $(LOGS)
-	@echo "Checking log for \"ERROR:\"..."
-	@! grep "ERROR:" $^
-	@echo "Checking log for \"SUCCESS:\"..."
-	@grep "SUCCESS:" $^
+	@! grep -q "ERROR" $^
+	@grep -q "SUCCESS" $^
 
 clean:
 	rm -rf *.vcd *.log *.out *.hex