test: small improvements to coverage

.golangci.yaml

@@ -1,5 +1,5 @@
 run:
-  go: "1.21"
+  go: "1.22"
   timeout: 10m
 linters:
   disable-all: true

apply_test.go

@@ -1,6 +1,8 @@
 package jsondiff
 
-import "testing"
+import (
+	"testing"
+)
 
 func Test_toDotPath(t *testing.T) {
 	for _, tc := range []struct {
@@ -80,3 +82,12 @@ func Test_isArrayIndex(t *testing.T) {
 		}
 	}
 }
+
+func TestPatch_apply_invalidJSON(t *testing.T) {
+	badJSON := []byte(`{"example":2:]}}`)
+
+	var p Patch
+	if _, err := p.apply(badJSON, true); err == nil {
+		t.Errorf("expected non-nil error")
+	}
+}

compare.go

@@ -34,11 +34,8 @@ func CompareWithoutMarshal(source, target interface{}, opts ...Option) (patch Pa
 
 	defer func() {
 		if r := recover(); r != nil {
-			if e, ok := r.(invalidJSONTypeError); ok {
-				err = e
-			} else {
-				err = fmt.Errorf("recovered from panic: %q", r)
-			}
+			e := r.(invalidJSONTypeError)
+			err = fmt.Errorf("jsondiff: invalid json type: %T", e.t)
 			patch = nil
 		}
 	}()

compare_test.go

@@ -1,6 +1,7 @@
 package jsondiff
 
 import (
+	"bytes"
 	"encoding/json"
 	"errors"
 	"testing"
@@ -31,7 +32,7 @@ func Test_marshalUnmarshal_invalid_JSON(t *testing.T) {
 	})
 }
 
-func TestCompareWithoutMarshal(t *testing.T) {
+func TestCompareWithoutMarshal_error(t *testing.T) {
 	type custom struct {
 		foo string
 		bar int
@@ -42,3 +43,49 @@ func TestCompareWithoutMarshal(t *testing.T) {
 	}
 	t.Log(err)
 }
+
+type skip struct{}
+
+var skipBytes = []byte("skip")
+
+func Test_compare_marshaling_error(t *testing.T) {
+	e := errors.New("")
+
+	d := Differ{opts: options{
+		marshal: func(a any) ([]byte, error) {
+			if _, ok := a.(skip); ok {
+				return skipBytes, nil
+			}
+			return nil, e
+		},
+		unmarshal: func(b []byte, _ any) error {
+			if bytes.Equal(b, skipBytes) {
+				return nil
+			}
+			return e
+		},
+	}}
+	if _, err := compare(&d, nil, nil); !errors.Is(err, e) {
+		t.Errorf("expected non-nil error")
+	}
+	if _, err := compare(&d, skip{}, nil); !errors.Is(err, e) {
+		t.Errorf("expected non-nil error")
+	}
+}
+
+func Test_compareJSON_marshaling_error(t *testing.T) {
+	e := errors.New("")
+
+	unmarshalFn := func(b []byte, _ any) error {
+		if bytes.Equal(b, skipBytes) {
+			return nil
+		}
+		return e
+	}
+	if _, err := compareJSON(nil, nil, nil, unmarshalFn); !errors.Is(err, e) {
+		t.Errorf("expected non-nil error")
+	}
+	if _, err := compareJSON(nil, []byte("skip"), nil, unmarshalFn); !errors.Is(err, e) {
+		t.Errorf("expected non-nil error")
+	}
+}

equal.go

@@ -2,18 +2,13 @@ package jsondiff
 
 import (
 	"encoding/json"
-	"fmt"
 	"strconv"
 )
 
 type invalidJSONTypeError struct {
 	t any
 }
 
-func (e invalidJSONTypeError) Error() string {
-	return fmt.Sprintf("jsondiff: invalid json type: %T", e.t)
-}
-
 // jsonValueType represents the type of JSON value.
 // It follows the types of values stored by json.Unmarshal
 // in interface values.
@@ -122,8 +117,9 @@ func deepEqualValue(src, tgt interface{}) bool {
 			}
 		}
 		return true
+	default:
+		panic("unexpected json type")
 	}
-	return false
 }
 
 var jsonTypeNames = []string{