metadata   map[string]string
		shouldFail bool
	}{
		// Validate if there a known 'content-type'.
		{
			header: http.Header{
				"Content-Type": []string{"image/png"},
			},
			metadata: map[string]string{
				"content-type": "image/png",
			},
			shouldFail: false,
		},
		// Validate if there are no keys to extract.
		{
			header: http.Header{
				"Test-1": []string{"123"},
			},