Add test for binary marker parsing

gitdiff/parser_binary_test.go

@@ -0,0 +1,54 @@
+package gitdiff
+
+import (
+	"io"
+	"testing"
+)
+
+func TestParseBinaryMarker(t *testing.T) {
+	tests := map[string]struct {
+		Input    string
+		IsBinary bool
+		HasData  bool
+		Err      bool
+	}{
+		"binaryPatch": {
+			Input:    "GIT binary patch\n",
+			IsBinary: true,
+			HasData:  true,
+		},
+		"binaryFileNoPatch": {
+			Input:    "Binary files differ\n",
+			IsBinary: true,
+			HasData:  false,
+		},
+		"textFile": {
+			Input:    "@@ -10,14 +22,31 @@\n",
+			IsBinary: false,
+			HasData:  false,
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			p := newTestParser(test.Input, true)
+
+			isBinary, hasData, err := p.ParseBinaryMarker()
+			if test.Err {
+				if err != nil || err == io.EOF {
+					t.Fatalf("expected error parsing binary marker, but got %v", err)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error parsing binary marker: %v", err)
+			}
+			if test.IsBinary != isBinary {
+				t.Errorf("incorrect isBinary value: expected %t, actual %t", test.IsBinary, isBinary)
+			}
+			if test.HasData != hasData {
+				t.Errorf("incorrect hasData value: expected %t, actual %t", test.HasData, hasData)
+			}
+		})
+	}
+}