1 files changed, 131 insertions, 0 deletions
diff --git a/src/internal/coverage/slicewriter/slw_test.go b/src/internal/coverage/slicewriter/slw_test.go
new file mode 100644
index 0000000..f4e75f4
--- /dev/null
+++ b/src/internal/coverage/slicewriter/slw_test.go
@@ -0,0 +1,131 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package slicewriter
+
+import (
+	"io"
+	"testing"
+)
+
+func TestSliceWriter(t *testing.T) {
+
+	sleq := func(t *testing.T, got []byte, want []byte) {
+		t.Helper()
+		if len(got) != len(want) {
+			t.Fatalf("bad length got %d want %d", len(got), len(want))
+		}
+		for i := range got {
+			if got[i] != want[i] {
+				t.Fatalf("bad read at %d got %d want %d", i, got[i], want[i])
+			}
+		}
+	}
+
+	wf := func(t *testing.T, ws *WriteSeeker, p []byte) {
+		t.Helper()
+		nw, werr := ws.Write(p)
+		if werr != nil {
+			t.Fatalf("unexpected write error: %v", werr)
+		}
+		if nw != len(p) {
+			t.Fatalf("wrong amount written want %d got %d", len(p), nw)
+		}
+	}
+
+	rf := func(t *testing.T, ws *WriteSeeker, p []byte) {
+		t.Helper()
+		b := make([]byte, len(p))
+		nr, rerr := ws.Read(b)
+		if rerr != nil {
+			t.Fatalf("unexpected read error: %v", rerr)
+		}
+		if nr != len(p) {
+			t.Fatalf("wrong amount read want %d got %d", len(p), nr)
+		}
+		sleq(t, b, p)
+	}
+
+	sk := func(t *testing.T, ws *WriteSeeker, offset int64, whence int) {
+		t.Helper()
+		_, err := ws.Seek(offset, whence)
+		if err != nil {
+			t.Fatalf("unexpected seek error: %v", err)
+		}
+	}
+
+	wp1 := []byte{1, 2}
+	ws := &WriteSeeker{}
+
+	// write some stuff
+	wf(t, ws, wp1)
+	// check that BytesWritten returns what we wrote.
+	sleq(t, ws.BytesWritten(), wp1)
+	// offset is at end of slice, so reading should return zero bytes.
+	rf(t, ws, []byte{})
+
+	// write some more stuff
+	wp2 := []byte{7, 8, 9}
+	wf(t, ws, wp2)
+	// check that BytesWritten returns what we expect.
+	wpex := []byte{1, 2, 7, 8, 9}
+	sleq(t, ws.BytesWritten(), wpex)
+	rf(t, ws, []byte{})
+
+	// seeks and reads.
+	sk(t, ws, 1, io.SeekStart)
+	rf(t, ws, []byte{2, 7})
+	sk(t, ws, -2, io.SeekCurrent)
+	rf(t, ws, []byte{2, 7})
+	sk(t, ws, -4, io.SeekEnd)
+	rf(t, ws, []byte{2, 7})
+
+	// seek back and overwrite
+	sk(t, ws, 1, io.SeekStart)
+	wf(t, ws, []byte{9, 11})
+	wpex = []byte{1, 9, 11, 8, 9}
+	sleq(t, ws.BytesWritten(), wpex)
+
+	// seeks on empty writer.
+	ws2 := &WriteSeeker{}
+	sk(t, ws2, 0, io.SeekStart)
+	sk(t, ws2, 0, io.SeekCurrent)
+	sk(t, ws2, 0, io.SeekEnd)
+
+	// check for seek errors.
+	_, err := ws.Seek(-1, io.SeekStart)
+	if err == nil {
+		t.Fatalf("expected error on invalid -1 seek")
+	}
+	_, err = ws.Seek(int64(len(ws.BytesWritten())), io.SeekStart)
+	if err == nil {
+		t.Fatalf("expected error on invalid %d seek", len(ws.BytesWritten()))
+	}
+
+	ws.Seek(0, io.SeekStart)
+	_, err = ws.Seek(-1, io.SeekCurrent)
+	if err == nil {
+		t.Fatalf("expected error on invalid -1 seek")
+	}
+	_, err = ws.Seek(int64(len(ws.BytesWritten())), io.SeekCurrent)
+	if err == nil {
+		t.Fatalf("expected error on invalid %d seek", len(ws.BytesWritten()))
+	}
+
+	_, err = ws.Seek(1, io.SeekEnd)
+	if err == nil {
+		t.Fatalf("expected error on invalid 1 seek")
+	}
+	bsamt := int64(-1*len(ws.BytesWritten()) - 1)
+	_, err = ws.Seek(bsamt, io.SeekEnd)
+	if err == nil {
+		t.Fatalf("expected error on invalid %d seek", bsamt)
+	}
+
+	// bad seek mode
+	_, err = ws.Seek(-1, io.SeekStart+9)
+	if err == nil {
+		t.Fatalf("expected error on invalid seek mode")
+	}
+}