1 files changed, 93 insertions, 0 deletions
diff --git a/internal/entropy/entropy_test.go b/internal/entropy/entropy_test.go
new file mode 100644
index 0000000..4ee1a6b
--- /dev/null
+++ b/internal/entropy/entropy_test.go
@@ -0,0 +1,93 @@
+package entropy
+
+import (
+	"bytes"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestHybridReaderMixesBaseAndExternal(t *testing.T) {
+	base := strings.NewReader(strings.Repeat("a", 4096))
+	external := strings.NewReader(strings.Repeat("b", 4096))
+	reader, err := NewHybridReader(base, external, HybridOptions{})
+	if err != nil {
+		t.Fatalf("NewHybridReader returned error: %v", err)
+	}
+
+	out := make([]byte, 128)
+	if _, err := io.ReadFull(reader, out); err != nil {
+		t.Fatalf("Read returned error: %v", err)
+	}
+
+	if bytes.Equal(out, bytes.Repeat([]byte("a"), len(out))) {
+		t.Fatalf("hybrid output matched raw base reader")
+	}
+	if reader.Degraded() {
+		t.Fatalf("hybrid reader degraded with enough external bytes")
+	}
+}
+
+func TestHybridReaderDegradesToBaseWhenExternalFails(t *testing.T) {
+	base := strings.NewReader(strings.Repeat("x", 4096))
+	external := strings.NewReader("")
+	reader, err := NewHybridReader(base, external, HybridOptions{})
+	if err != nil {
+		t.Fatalf("NewHybridReader returned error: %v", err)
+	}
+
+	out := make([]byte, 32)
+	if _, err := io.ReadFull(reader, out); err != nil {
+		t.Fatalf("Read returned error: %v", err)
+	}
+
+	if !bytes.Equal(out, bytes.Repeat([]byte("x"), len(out))) {
+		t.Fatalf("degraded output should come from base reader")
+	}
+	if !reader.Degraded() {
+		t.Fatalf("hybrid reader should report degraded state")
+	}
+	if reader.DegradeError() == nil {
+		t.Fatalf("hybrid reader should keep the external source error")
+	}
+}
+
+func TestHybridReaderBuffersSmallReads(t *testing.T) {
+	base := strings.NewReader(strings.Repeat("a", blockSize))
+	external := strings.NewReader(strings.Repeat("b", blockSize))
+	reader, err := NewHybridReader(base, external, HybridOptions{})
+	if err != nil {
+		t.Fatalf("NewHybridReader returned error: %v", err)
+	}
+
+	var one [1]byte
+	for i := 0; i < blockSize; i++ {
+		if _, err := io.ReadFull(reader, one[:]); err != nil {
+			t.Fatalf("Read %d returned error: %v", i, err)
+		}
+	}
+
+	if reader.Degraded() {
+		t.Fatalf("small reads should reuse one mixed block before reading external again")
+	}
+}
+
+func TestHybridReaderRequiresExternalWhenConfigured(t *testing.T) {
+	base := strings.NewReader(strings.Repeat("x", 4096))
+	external := strings.NewReader("")
+	reader, err := NewHybridReader(base, external, HybridOptions{RequireExternal: true})
+	if err != nil {
+		t.Fatalf("NewHybridReader returned error: %v", err)
+	}
+
+	out := make([]byte, 1)
+	if _, err := io.ReadFull(reader, out); err == nil {
+		t.Fatalf("Read returned nil error with required external entropy")
+	}
+}
+
+func TestNewHybridReaderRejectsMissingExternalSource(t *testing.T) {
+	if _, err := NewHybridReader(strings.NewReader("base"), nil, HybridOptions{}); err != ErrExternalEntropyRequired {
+		t.Fatalf("NewHybridReader error = %v, want %v", err, ErrExternalEntropyRequired)
+	}
+}