Add a test for the EOF behaviour of Read.

memfile_test.go

diff --git a/memfile_test.go b/memfile_test.go
new file mode 100644
index 0000000..b77ae8e
--- /dev/null
+++ b/memfile_test.go
@@ -0,0 +1,27 @@
+package afero
+
+import (
+	"io"
+	"testing"
+)
+
+func TestMemFileRead(t *testing.T) {
+	f := MemFileCreate("testfile")
+	f.WriteString("abcd")
+	f.Seek(0, 0)
+	b := make([]byte, 8)
+	n, err := f.Read(b)
+	if n != 4 {
+		t.Errorf("didn't read all bytes: %v %v %v", n, err, b)
+	}
+	if err != nil {
+		t.Errorf("err is not nil: %v %v %v", n, err, b)
+	}
+	n, err = f.Read(b)
+	if n != 0 {
+		t.Errorf("read more bytes: %v %v %v", n, err, b)
+	}
+	if err != io.EOF {
+		t.Errorf("error is not EOF: %v %v %v", n, err, b)
+	}
+}