# imports
import pytest  # used for our unit tests
from sentry_sdk.metrics import _serialize_tags

# unit tests

def test_empty_input():
    # Test with None
    assert _serialize_tags(None) == ()
    # Test with empty dictionary
    assert _serialize_tags({}) == ()

def test_single_key_value_pair():
    # Test with a single key-value pair
    assert _serialize_tags({'key1': 'value1'}) == (('key1', 'value1'),)
    # Test with an integer value
    assert _serialize_tags({'key1': 123}) == (('key1', '123'),)

def test_multiple_key_value_pairs():
    # Test with multiple key-value pairs
    assert _serialize_tags({'key1': 'value1', 'key2': 'value2'}) == (('key1', 'value1'), ('key2', 'value2'))
    # Test with mixed types of values
    assert _serialize_tags({'key1': 123, 'key2': 456}) == (('key1', '123'), ('key2', '456'))

def test_values_as_collections():
    # Test with list values
    assert _serialize_tags({'key1': ['value1', 'value2']}) == (('key1', 'value1'), ('key1', 'value2'))
    # Test with tuple values
    assert _serialize_tags({'key1': ('value1', 'value2')}) == (('key1', 'value1'), ('key1', 'value2'))
    # Test with list of integers
    assert _serialize_tags({'key1': [1, 2, 3]}) == (('key1', '1'), ('key1', '2'), ('key1', '3'))

def test_mixed_types_of_values():
    # Test with mixed types of values
    assert _serialize_tags({'key1': 'value1', 'key2': 123, 'key3': [1, 2, 3]}) == (('key1', 'value1'), ('key2', '123'), ('key3', '1'), ('key3', '2'), ('key3', '3'))
    assert _serialize_tags({'key1': 'value1', 'key2': ['value2', 3], 'key3': (4, 'value4')}) == (('key1', 'value1'), ('key2', '3'), ('key2', 'value2'), ('key3', '4'), ('key3', 'value4'))

def test_values_with_none():
    # Test with None values
    assert _serialize_tags({'key1': None}) == ()
    assert _serialize_tags({'key1': [None, 'value1', None]}) == (('key1', 'value1'),)
    assert _serialize_tags({'key1': 'value1', 'key2': None, 'key3': [None, 'value2']}) == (('key1', 'value1'), ('key3', 'value2'))

def test_unsorted_input():
    # Test with unsorted input
    assert _serialize_tags({'b': 'value2', 'a': 'value1'}) == (('a', 'value1'), ('b', 'value2'))
    assert _serialize_tags({'key2': 'value2', 'key1': 'value1'}) == (('key1', 'value1'), ('key2', 'value2'))

def test_duplicate_keys_with_collection_values():
    # Test with duplicate keys due to collection flattening
    assert _serialize_tags({'key1': ['value1', 'value2'], 'key1': 'value3'}) == (('key1', 'value1'), ('key1', 'value2'), ('key1', 'value3'))

def test_large_input():
    # Test with large input
    tags = {f'key{i}': f'value{i}' for i in range(1000)}
    expected = tuple((f'key{i}', f'value{i}') for i in range(1000))
    assert _serialize_tags(tags) == expected

    tags = {f'key{i}': [f'value{i}_1', f'value{i}_2'] for i in range(1000)}
    expected = tuple((f'key{i}', f'value{i}_1') for i in range(1000)) + tuple((f'key{i}', f'value{i}_2') for i in range(1000))
    assert _serialize_tags(tags) == expected

def test_special_characters_in_keys_and_values():
    # Test with special characters in keys and values
    assert _serialize_tags({'key!@#': 'value$%^'}) == (('key!@#', 'value$%^'),)
    assert _serialize_tags({'key1': 'value with spaces', 'key2': 'value_with_underscores'}) == (('key1', 'value with spaces'), ('key2', 'value_with_underscores'))

def test_non_string_keys():
    # Test with non-string keys
    assert _serialize_tags({123: 'value1'}) == (('123', 'value1'),)
    assert _serialize_tags({(1, 2): 'value2'}) == (('(1, 2)', 'value2'),)

def test_nested_collections():
    # Test with nested collections
    assert _serialize_tags({'key1': [['value1', 'value2'], 'value3']}) == (('key1', "['value1', 'value2']"), ('key1', 'value3'))
    assert _serialize_tags({'key1': (('value1',), 'value2')}) == (('key1', "('value1',)"), ('key1', 'value2'))

def test_empty_collections():
    # Test with empty collections
    assert _serialize_tags({'key1': []}) == ()
    assert _serialize_tags({'key1': (), 'key2': 'value2'}) == (('key2', 'value2'),)

def test_performance_and_scalability():
    # Test performance with large and complex inputs
    tags = {f'key{i}': [f'value{i}_{j}' for j in range(100)] for i in range(1000)}
    expected = tuple((f'key{i}', f'value{i}_{j}') for i in range(1000) for j in range(100))
    assert _serialize_tags(tags) == expected