diff --git a/rcap/run_test.go b/rcap/run_test.go
new file mode 100644
index 0000000..d35ff6f
--- /dev/null
+++ b/rcap/run_test.go
@@ -0,0 +1,173 @@
+package rcap
+
+import (
+	"errors"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/google/gopacket"
+)
+
+func TestNewRunner(t *testing.T) {
+	c := makeConfig()
+	_, err := NewRunner(c)
+	if err != nil {
+		t.Errorf("nil is expected, but got '%v'.", err)
+	}
+}
+
+func TestRunnerReloadWithFailure(t *testing.T) {
+	c := makeConfig()
+	r, _ := NewRunner(c)
+
+	// empty config file
+	if err := r.Reload(); err == nil {
+		t.Error("err is expected, but got 'nil'.")
+	}
+
+	// invalid config
+	c.Filename = "testdata/rcap-invalid-config.toml"
+	if err := r.Reload(); err == nil {
+		t.Error("err is expected, but got 'nil'.")
+	}
+}
+
+func TestRunnerReload(t *testing.T) {
+	c := makeConfig()
+	r, _ := NewRunner(c)
+
+	// valid config
+	c.Filename = "testdata/rcap-good.toml"
+	if err := r.Reload(); err != nil {
+		t.Errorf("nil is expected, but got '%v'.", err)
+	}
+
+	// check if config values are updated.
+	if c.Rcap.BpfRules == r.config.Rcap.BpfRules {
+		t.Error("config is not updated.")
+	}
+}
+
+func TestRunnerSetupReaderAndWriter(t *testing.T) {
+	c := makeConfig()
+	c.Rcap.FileFmt = filepath.Join(t.TempDir(), "traffic-%Y%m%d-%H%M%S.pcap")
+	c.CheckAndFormat()
+	r, _ := NewRunner(c)
+
+	// NewReader fails.
+	if err := r.setupReaderAndWriter(); err == nil {
+		t.Error("err is expected, but got 'nil'.")
+	}
+
+	// NewReader and NewWriter succeed (reader is a dummy).
+	r.reader, _ = openAndSetUpReader(c, "testdata/sample.pcap")
+	if err := r.setupReaderAndWriter(); err != nil {
+		t.Error("err is expected, but got 'nil'.")
+	}
+}
+
+func TestRunnerGetTimestamp(t *testing.T) {
+	c := makeConfig()
+	c.CheckAndFormat()
+	r, _ := NewRunner(c)
+
+	metadata := gopacket.CaptureInfo{
+		Timestamp: time.Unix(86400, 0),
+	}
+	pkterr := errors.New("dummy error")
+
+	// Timestamp is from system time because of UseSystemTime.
+	c.Rcap.UseSystemTime = true
+	if ts := r.getTimestamp(metadata, nil); ts < 1688137200 {
+		t.Error("'ts' is not from system time (UseSystemTime=true).")
+	}
+
+	// Timestamp is from system time because of pkterr.
+	c.Rcap.UseSystemTime = false
+	if ts := r.getTimestamp(metadata, pkterr); ts < 1688137200 {
+		t.Error("'ts' is not from system time (UseSystemTime=false, pkterr!=nil).")
+	}
+
+	// Timestamp is from metadata.
+	if ts := r.getTimestamp(metadata, nil); ts != 86400 {
+		t.Errorf("'ts' is expected to be '%v', but got '%v'.", 86400, ts)
+	}
+}
+
+func TestRunnerIsSamplingMode(t *testing.T) {
+	c := makeConfig()
+	c.Rcap.Sampling = 1.0
+	c.CheckAndFormat()
+	r, _ := NewRunner(c)
+
+	if r.isSamplingMode() != false {
+		t.Error("'false' is expected, but got 'true'.")
+	}
+
+	c.Rcap.Sampling = 0.5
+	c.CheckAndFormat()
+
+	if r.isSamplingMode() != true {
+		t.Error("'true' is expected, but got 'false'.")
+	}
+}
+
+func TestRunnerDoSample(t *testing.T) {
+	c := makeConfig()
+	c.Rcap.Sampling = 0.1
+	c.CheckAndFormat()
+	r, _ := NewRunner(c)
+
+	count := 0
+	for i := 0; i < 100; i++ {
+		if r.doSample() {
+			count++
+		}
+	}
+
+	if !(count < 30) {
+		t.Errorf("The probability of doSample seems to be invalid: (%v > 30)", count)
+	}
+}
+
+func TestRunnerRunWithFailure(t *testing.T) {
+	tempDir := t.TempDir()
+	c := makeConfig()
+	c.Rcap.FileFmt = filepath.Join(tempDir, "traffic-%Y%m%d-%H%M%S.pcap")
+	c.CheckAndFormat()
+	r, _ := NewRunner(c)
+
+	// setupReaderAndWriter fails because of Device = 'any'.
+	if err := r.Run(); err == nil {
+		t.Error("err is expected, but got 'nil'.")
+	}
+}
+
+func TestRunnerRun(t *testing.T) {
+	tempDir := t.TempDir()
+	c := makeConfig()
+	c.Rcap.FileFmt = filepath.Join(tempDir, "traffic-%Y%m%d-%H%M%S.pcap")
+	c.CheckAndFormat()
+	r, _ := NewRunner(c)
+	r.reader, _ = openAndSetUpReader(c, "testdata/sample.pcap")
+
+	// EOF error.
+	if err := r.Run(); err == nil {
+		t.Error("err is expected, but got 'nil'.")
+	}
+}
+
+func TestRunnerClose(t *testing.T) {
+	// Setup reader and writer to be closed.
+	tempDir := t.TempDir()
+	c := makeConfig()
+	c.Rcap.FileFmt = filepath.Join(tempDir, "traffic-%Y%m%d-%H%M%S.pcap")
+	c.CheckAndFormat()
+	r, _ := NewRunner(c)
+	r.reader, _ = openAndSetUpReader(c, "testdata/sample.pcap")
+	r.writer, _ = NewWriter(c, r.reader.LinkType())
+	r.writer.openWriter(0)
+
+	r.Close()
+}