diff --git a/pkg/ioutils/buffer_test.go b/pkg/ioutils/buffer_test.go
index 8bf5ae64ea..f687124386 100644
--- a/pkg/ioutils/buffer_test.go
+++ b/pkg/ioutils/buffer_test.go
@@ -5,6 +5,81 @@ import (
 	"testing"
 )
 
+func TestFixedBufferCap(t *testing.T) {
+	buf := &fixedBuffer{buf: make([]byte, 0, 5)}
+
+	n := buf.Cap()
+	if n != 5 {
+		t.Fatalf("expected buffer capacity to be 5 bytes, got %d", n)
+	}
+}
+
+func TestFixedBufferLen(t *testing.T) {
+	buf := &fixedBuffer{buf: make([]byte, 0, 10)}
+
+	buf.Write([]byte("hello"))
+	l := buf.Len()
+	if l != 5 {
+		t.Fatalf("expected buffer length to be 5 bytes, got %d", l)
+	}
+
+	buf.Write([]byte("world"))
+	l = buf.Len()
+	if l != 10 {
+		t.Fatalf("expected buffer length to be 10 bytes, got %d", l)
+	}
+
+	// read 5 bytes
+	b := make([]byte, 5)
+	buf.Read(b)
+
+	l = buf.Len()
+	if l != 5 {
+		t.Fatalf("expected buffer length to be 5 bytes, got %d", l)
+	}
+
+	n, err := buf.Write([]byte("i-wont-fit"))
+	if n != 0 {
+		t.Fatalf("expected no bytes to be written to buffer, got %d", n)
+	}
+	if err != errBufferFull {
+		t.Fatalf("expected errBufferFull, got %v", err)
+	}
+
+	l = buf.Len()
+	if l != 5 {
+		t.Fatalf("expected buffer length to still be 5 bytes, got %d", l)
+	}
+
+	buf.Reset()
+	l = buf.Len()
+	if l != 0 {
+		t.Fatalf("expected buffer length to still be 0 bytes, got %d", l)
+	}
+}
+
+func TestFixedBufferString(t *testing.T) {
+	buf := &fixedBuffer{buf: make([]byte, 0, 10)}
+
+	buf.Write([]byte("hello"))
+	buf.Write([]byte("world"))
+
+	out := buf.String()
+	if out != "helloworld" {
+		t.Fatalf("expected output to be \"helloworld\", got %q", out)
+	}
+
+	// read 5 bytes
+	b := make([]byte, 5)
+	buf.Read(b)
+
+	// test that fixedBuffer.String() only returns the part that hasn't been read
+	out = buf.String()
+	if out != "world" {
+		t.Fatalf("expected output to be \"world\", got %q", out)
+	}
+}
+
 func TestFixedBufferWrite(t *testing.T) {
 	buf := &fixedBuffer{buf: make([]byte, 0, 64)}
 	n, err := buf.Write([]byte("hello"))