components/Tabs/tests/unit/MaterialTabsTests.m

// Copyright 2017-present the Material Components for iOS authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#import <XCTest/XCTest.h>

#import "MaterialTabs.h"

@interface MaterialTabsTests : XCTestCase
@end

@implementation MaterialTabsTests {
  MDCTabBar *_tabBar;
  UITabBarItem *_itemA;
  UITabBarItem *_itemB;
  UITabBarItem *_itemC;
}

- (void)setUp {
  [super setUp];

  _tabBar = [[MDCTabBar alloc] init];
  _itemA = [[UITabBarItem alloc] initWithTitle:@"A" image:nil tag:0];
  _itemB = [[UITabBarItem alloc] initWithTitle:@"B" image:nil tag:0];
  _itemC = [[UITabBarItem alloc] initWithTitle:@"C" image:nil tag:0];
}

- (void)tearDown {
  _itemA = nil;
  _itemB = nil;
  _itemC = nil;
  _tabBar = nil;

  [super tearDown];
}

/// Tab bars should by default select the first item in their items array.
- (void)testSelectsFirstItemByDefault {
  _tabBar.items = @[ _itemA, _itemB, _itemC ];
  XCTAssertEqual(_tabBar.selectedItem, _itemA);
}

/// Tab bars should preserve their selection if possible when changing items.
- (void)testPreservesSelectedItem {
  // Set items {A, B} which should select item A
  _tabBar.items = @[ _itemA, _itemB ];

  // Set items {C, A} which should preserve the selection of A.
  _tabBar.items = @[ _itemC, _itemA ];
  XCTAssertEqual(_tabBar.selectedItem, _itemA);
}

/// Tab bars should select the first item if the old selection is no longer present.
- (void)testSelectsFirstWhenSelectedItemMissing {
  // Set items {A, B} which should select item A
  _tabBar.items = @[ _itemA, _itemB ];

  // Set items not including A, which should select B.
  _tabBar.items = @[ _itemB, _itemC ];
  XCTAssertEqual(_tabBar.selectedItem, _itemB);
}

/// Tab bars should safely accept having their items set to the empty array.
- (void)testSafelyHandlesEmptyItems {
  _tabBar.items = @[];
  XCTAssertNil(_tabBar.selectedItem);

  // Setting the empty array should also be safe coming from a non-empty array.
  _tabBar.items = @[ _itemA ];
  _tabBar.items = @[];
  XCTAssertNil(_tabBar.selectedItem);
}

// Setting items to the same set of items should change nothing.
- (void)testItemsUpdateIsIdempotent {
  // Start with {A, B}, which selects A.
  _tabBar.items = @[ _itemA, _itemB ];
  XCTAssertEqual(_tabBar.selectedItem, _itemA);

  // Remove A, which selects B.
  _tabBar.items = @[ _itemB ];
  XCTAssertEqual(_tabBar.selectedItem, _itemB);

  // Set same set of items, which should make no difference to the selection.
  _tabBar.items = @[ _itemB ];
  XCTAssertEqual(_tabBar.selectedItem, _itemB);
}

// TODO(#5199): Add a snapshot test to prove the tabs render without a window

@end