Added cursor tests

cursor/cursor_test.go

@@ -0,0 +1,92 @@
+package cursor_test
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"git.codemonkeysoftware.net/b/gigaparsec/cursor"
+	"github.com/shoenig/test"
+	"github.com/shoenig/test/must"
+	"pgregory.net/rapid"
+)
+
+func Todo(t *testing.T) {
+	t.Errorf("TODO")
+}
+
+func SliceOfNZero[T any](minLen, maxLen int) *rapid.Generator[[]T] {
+	return rapid.Map(rapid.IntRange(minLen, maxLen), func(n int) []T {
+		return make([]T, n)
+	})
+}
+
+func testCursor[C cursor.Cursor[byte]](t *testing.T, makeCursor func([]byte) C) {
+	t.Helper()
+	t.Run("cursor reads the same position every time", rapid.MakeCheck(func(t *rapid.T) {
+		data := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "data")
+		dst := SliceOfNZero[byte](0, len(data)-1).Draw(t, "dst")
+		expected := data[:len(dst)]
+		c := makeCursor(data)
+
+		_, next, err := c.Read(dst)
+		must.NoError(t, err)
+		must.SliceEqOp(t, expected, dst)
+
+		next.Read(dst)
+		_, _, err = c.Read(dst)
+		must.NoError(t, err)
+		must.SliceEqOp(t, expected, dst)
+	}))
+	t.Run("Read returns io.EOF iff it overruns source", rapid.MakeCheck(func(t *rapid.T) {
+		data := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "data")
+		dst := SliceOfNZero[byte](0, 200).Draw(t, "dst")
+		c := makeCursor(data)
+
+		n, _, err := c.Read(dst)
+		t.Logf("n=%d", n)
+		must.EqOp(t, min(len(data), len(dst)), int(n))
+		if len(dst) > len(data) || c.Pos() == uint64(len(data)) {
+			must.ErrorIs(t, err, io.EOF)
+		} else {
+			must.NoError(t, err)
+		}
+	}))
+	t.Run("next cursor reads next input", rapid.MakeCheck(func(t *rapid.T) {
+		const maxLen = 100
+		data := rapid.SliceOfN(rapid.Byte(), 1, maxLen).Draw(t, "data")
+		skip := rapid.IntRange(0, len(data)-1).Draw(t, "data")
+		c := makeCursor(data)
+
+		_, next, err := c.Read(make([]byte, skip))
+		must.NoError(t, err)
+		must.EqOp(t, skip, int(next.Pos()))
+		dst := make([]byte, maxLen)
+		n, _, _ := next.Read(dst)
+		must.SliceEqOp(t, data[skip:skip+int(n)], dst[:n])
+	}))
+	t.Run("Read returns an error if n is less than requested", rapid.MakeCheck(func(t *rapid.T) {
+		data := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "data")
+		c := makeCursor(data)
+
+		n, _, err := c.Read(make([]byte, len(data)+1))
+		test.ErrorIs(t, err, io.EOF)
+		test.EqOp(t, len(data), int(n))
+	}))
+}
+
+func TestSliceCursor(t *testing.T) {
+	testCursor(t, cursor.NewSlice[byte])
+}
+
+func TestStringCursor(t *testing.T) {
+	testCursor(t, func(b []byte) cursor.StringCursor {
+		return cursor.NewString(string(b))
+	})
+}
+
+func TestReaderAtCursor(t *testing.T) {
+	testCursor(t, func(b []byte) cursor.ReaderAtCursor {
+		return cursor.NewReaderAt(bytes.NewReader(b))
+	})
+}