[image_picker] Add native tests for image, metadata, photo-asset, and PHPicker save utilities

[victogomez-cs]

Adds native unit tests for previously untested paths in FLTImagePickerImageUtil, FLTImagePickerMetaDataUtil, FLTImagePickerPhotoAssetUtil, and FLTPHPickerSaveImageToPathOperation before the Objective-C → Swift migration. Production code is unchanged.

This is a tests-only change, so it does not bump the package version or CHANGELOG.

Native RunnerTests go from 72 tests to 88 tests (+16).

New test cases

ImageUtilTests:

• testScaledGIFImage_UsesClampedDelayWhenUnclampedDelayMissing — GIF scaling uses the clamped delay when unclamped delay is missing

MetaDataUtilTests:

• testGetImageMIMETypeFromImageDataUnknownReturnsOther — unrecognized image bytes map to the Other MIME type
• testConvertImageIgnoresQualityForPNG — PNG conversion ignores JPEG quality and stays PNG
• testConvertImageDefaultsNonJPEGNonPNGToJPEG — GIF and other non-JPEG/PNG data convert to JPEG

PhotoAssetUtilTests:

• testGetAssetFromImagePickerInfoShouldReturnNilIfNotAvailable — picker info without a PHAsset returns nil
• testGetAssetFromImagePickerInfoShouldReturnAssetIfPresent — picker info with a PHAsset returns that asset
• testSaveVideoFromURLReturnsNilWhenSourceIsUnreadable — missing source file returns nil
• testSaveVideoFromURLCopiesReadableFile — a readable video is copied to a new path
• testSaveVideoFromURLReturnsNilWhenCopyFails — copy failure returns nil
• testSaveImageWithOriginalImageDataNilUsesDefaultJPEG — nil original data saves as .jpg
• testCreateFileReturnsPathWhenWriteFails — create-file still returns a path when the write fails

PickerSaveImageToPathOperationTests:

• testInitWithNilResultReturnsNil — nil PHPicker result does not create an operation
• testStartWhenCancelledFinishesWithoutSaving — a cancelled operation finishes without calling the save callback
• testSaveVideoCopiesFile — a video item is copied to the saved path
• testSaveVideoFailsWhenLoadReturnsError — a load error is reported as invalid_image
• testSaveVideoFailsWhenCopyFails — a copy error is reported as flutter_image_picker_copy_video_error

First part of image_picker_ios coverage backfill before the Obj-C → Swift migration for flutter/flutter#119107

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
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• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style, or I have commented below to indicate which documented exception this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

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[gemini-code-assist]

Code Review

This pull request adds comprehensive unit tests for image, metadata, photo asset, and path operation utilities in the iOS image picker package. The review feedback highlights opportunities to improve test robustness and hygiene, specifically by cleaning up temporary files and guarding against potential crashes caused by passing nil URLs to file management APIs.

[gemini-code-assist]

If saveVideoFromURL: returns nil, destination will be nil. Passing a nil URL to removeItemAtURL:error: throws an NSInvalidArgumentException and will crash the test runner instead of failing the test gracefully. We should guard the cleanup call and the file existence check to ensure they only run if destination is non-nil.

  XCTAssertNotNil(destination);
  if (destination) {
    XCTAssertTrue([[NSFileManager defaultManager] fileExistsAtPath:destination.path]);
  }
  [[NSFileManager defaultManager] removeItemAtPath:sourcePath error:nil];
  if (destination) {
    [[NSFileManager defaultManager] removeItemAtURL:destination error:nil];
  }

[victogomez-cs]

Fixed! Good catch, XCTAssertNotNil doesn’t abort the test, so removeItemAtURL: could be called with nil and throw. Guarded the existence check and cleanup so they only run when destination is non-nil

[gemini-code-assist]

The temporary file created at savedPath is not cleaned up after the test completes, which leaks files in the temporary directory. We should remove the file at savedPath at the end of the test.

  XCTAssertEqualObjects([NSURL fileURLWithPath:savedPath].pathExtension, @"jpg");
  if (savedPath) {
    [[NSFileManager defaultManager] removeItemAtPath:savedPath error:nil];
  }
}

[victogomez-cs]

Agreed and fixed. The test now removes savedPath after the assertion.

[gemini-code-assist]

The temporary file created at savedPath by the operation is not cleaned up, leaking files in the temporary directory. We should delete the file at savedPath inside the completion block.

Suggested change

	savedPathBlock:^(NSString *savedPath, FlutterError *error) {
	XCTAssertNil(error);
	XCTAssertTrue([[NSFileManager defaultManager] fileExistsAtPath:savedPath]);
	[pathExpectation fulfill];
	}];
	savedPathBlock:^(NSString *savedPath, FlutterError *error) {
	XCTAssertNil(error);
	XCTAssertTrue([[NSFileManager defaultManager] fileExistsAtPath:savedPath]);
	if (savedPath) {
	[[NSFileManager defaultManager] removeItemAtPath:savedPath error:nil];
	}
	[pathExpectation fulfill];
	}];

[victogomez-cs]

Agreed and fixed. The copied file is now deleted after the operation finishes (in addition to the source .mov).