toContain()

in packages/expect/src/matchers.ts [449:551]
92 lines of code
15 McCabe index (conditional complexity)

  toContain(received: ContainIterable | string, expected: unknown) {
    const matcherName = 'toContain';
    const isNot = this.isNot;
    const options: MatcherHintOptions = {
      comment: 'indexOf',
      isNot,
      promise: this.promise,
    };

    if (received == null) {
      throw new Error(
        matcherErrorMessage(
          matcherHint(matcherName, undefined, undefined, options),
          `${RECEIVED_COLOR('received')} value must not be null nor undefined`,
          printWithType('Received', received, printReceived),
        ),
      );
    }

    if (typeof received === 'string') {
      const wrongTypeErrorMessage = `${EXPECTED_COLOR(
        'expected',
      )} value must be a string if ${RECEIVED_COLOR(
        'received',
      )} value is a string`;

      if (typeof expected !== 'string') {
        throw new Error(
          matcherErrorMessage(
            matcherHint(matcherName, received, String(expected), options),
            wrongTypeErrorMessage,
            // eslint-disable-next-line prefer-template
            printWithType('Expected', expected, printExpected) +
              '\n' +
              printWithType('Received', received, printReceived),
          ),
        );
      }

      const index = received.indexOf(String(expected));
      const pass = index !== -1;

      const message = () => {
        const labelExpected = `Expected ${
          typeof expected === 'string' ? 'substring' : 'value'
        }`;
        const labelReceived = 'Received string';
        const printLabel = getLabelPrinter(labelExpected, labelReceived);

        return (
          // eslint-disable-next-line prefer-template
          matcherHint(matcherName, undefined, undefined, options) +
          '\n\n' +
          `${printLabel(labelExpected)}${isNot ? 'not ' : ''}${printExpected(
            expected,
          )}\n` +
          `${printLabel(labelReceived)}${isNot ? '    ' : ''}${
            isNot
              ? printReceivedStringContainExpectedSubstring(
                  received,
                  index,
                  String(expected).length,
                )
              : printReceived(received)
          }`
        );
      };

      return {message, pass};
    }

    const indexable = Array.from(received);
    const index = indexable.indexOf(expected);
    const pass = index !== -1;

    const message = () => {
      const labelExpected = 'Expected value';
      const labelReceived = `Received ${getType(received)}`;
      const printLabel = getLabelPrinter(labelExpected, labelReceived);

      return (
        // eslint-disable-next-line prefer-template
        matcherHint(matcherName, undefined, undefined, options) +
        '\n\n' +
        `${printLabel(labelExpected)}${isNot ? 'not ' : ''}${printExpected(
          expected,
        )}\n` +
        `${printLabel(labelReceived)}${isNot ? '    ' : ''}${
          isNot && Array.isArray(received)
            ? printReceivedArrayContainExpectedItem(received, index)
            : printReceived(received)
        }` +
        (!isNot &&
        indexable.findIndex(item =>
          equals(item, expected, [iterableEquality]),
        ) !== -1
          ? `\n\n${SUGGEST_TO_CONTAIN_EQUAL}`
          : '')
      );
    };

    return {message, pass};
  },