Ensure that process.IOStat is non-nil

checks/process.go

@@ -181,7 +181,7 @@ func formatIO(fp *process.FilledProcess, lastIO *process.IOCountersStat, before
 
 	diff := time.Now().Unix() - before.Unix()
 	if before.IsZero() || diff <= 0 {
-		return nil
+		return &model.IOStat{}
 	}
 	// Reading 0 as a counter means the file could not be opened due to permissions. We distinguish this from a real 0 in rates.
 	var readRate float32

checks/process_test.go

@@ -1,6 +1,7 @@
 package checks
 
 import (
+	"github.com/stretchr/testify/require"
 	"regexp"
 	"runtime"
 	"strings"
@@ -140,6 +141,39 @@ func TestRateCalculation(t *testing.T) {
 	assert.True(t, floatEquals(calculateRate(0, 1, prev), 0))
 }
 
+func TestFormatIO(t *testing.T) {
+	fp := &process.FilledProcess{
+		IOStat: &process.IOCountersStat{
+			ReadCount:  6,
+			WriteCount: 8,
+			ReadBytes:  10,
+			WriteBytes: 12,
+		},
+	}
+
+	last := &process.IOCountersStat{
+		ReadCount:  1,
+		WriteCount: 2,
+		ReadBytes:  3,
+		WriteBytes: 4,
+	}
+
+	// fp.IoStat is nil
+	assert.NotNil(t, formatIO(&process.FilledProcess{}, last, time.Now().Add(-2*time.Second)))
+
+	// Elapsed time < 1s
+	assert.NotNil(t, formatIO(fp, last, time.Now()))
+
+	result := formatIO(fp, last, time.Now().Add(-1*time.Second))
+	require.NotNil(t, result)
+
+	assert.Equal(t, float32(5), result.ReadRate)
+	assert.Equal(t, float32(6), result.WriteRate)
+	assert.Equal(t, float32(7), result.ReadBytesRate)
+	assert.Equal(t, float32(8), result.WriteBytesRate)
+
+}
+
 func floatEquals(a, b float32) bool {
 	var e float32 = 0.00000001 // Difference less than some epsilon
 	return a-b < e && b-a < e