/**
 * Asserts that the provided `projectId` conforms to Firestore / Google Cloud rules.
 *
 * @param projectId - The project ID to validate.
 * @returns The same `projectId` when valid (for fluent usage).
 * @throws {GoogleError} {@link Status.INTERNAL} when the project ID is invalid.
 */
export declare function assertValidProjectId(projectId: string): string;
/**
 * Asserts that a (possibly optional) value with a `length` property is non-empty.
 *
 * If `required` is `false` and the value is `undefined`/`null`, no error is thrown.
 *
 * @param argName - Name of the argument (for error messages).
 * @param value - The value to check; must have a numeric `length` when present.
 * @param required - Whether the argument is required.
 * @throws {GoogleError} {@link Status.INVALID_ARGUMENT} when required and empty/missing.
 */
export declare function assertNotEmpty(argName: string, value: {
    length: number;
} | undefined | null, required: boolean): void;
/**
 * Asserts that a value is an instance of a constructor or satisfies a predicate.
 *
 * If `required` is `false` and the value is `undefined`/`null`, no error is thrown.
 *
 * @param argName - Name of the argument (for error messages).
 * @param typeName - Human-readable type name for error messaging.
 * @param value - The value to validate.
 * @param type - Either a constructor function (for `instanceof`) or a predicate `(value) => boolean`.
 * @param required - Whether the argument is required.
 * @throws {GoogleError} {@link Status.INVALID_ARGUMENT} when validation fails.
 */
export declare function assertInstanceOf(argName: string, typeName: string, value: unknown, type: (new (...args: unknown[]) => unknown) | ((value: unknown) => boolean), required: boolean): void;
/**
 * Asserts that two arguments are mutually exclusive—i.e., not both specified.
 *
 * @param argName1 - Name of the first argument.
 * @param value1 - Value of the first argument.
 * @param argName2 - Name of the second argument.
 * @param value2 - Value of the second argument.
 * @throws {GoogleError} {@link Status.INVALID_ARGUMENT} when both are specified.
 */
export declare function assertMutuallyExclusive(argName1: string, value1: unknown, argName2: string, value2: unknown): void;
/**
 * Asserts that at least one of two alternative arguments is provided.
 *
 * @param argName1 - Name of the first argument.
 * @param value1 - Value of the first argument.
 * @param argName2 - Name of the second argument.
 * @param value2 - Value of the second argument.
 * @throws {GoogleError} {@link Status.INVALID_ARGUMENT} when both are missing.
 */
export declare function assertEitherRequired(argName1: string, value1: unknown, argName2: string, value2: unknown): void;
/**
 * Asserts that a request field is not supported in the mock and therefore must be absent.
 *
 * @param argName - Name of the unsupported request field.
 * @param value - The field value to check.
 * @throws {GoogleError} {@link Status.UNIMPLEMENTED} when the field is provided.
 */
export declare function assertRequestArgumentNotSupported(argName: string, value: unknown): void;
/**
 * Asserts that a required request field is present and returns it.
 *
 * @typeParam T - The expected type of the value.
 * @param argName - Name of the required field.
 * @param value - The value to check.
 * @returns The value when present.
 * @throws {GoogleError} {@link Status.INVALID_ARGUMENT} when the field is missing.
 */
export declare function assertRequestArgument<T>(argName: string, value: T | null | undefined): T;
/**
 * Asserts that a required field *within a fieldFilter* is present and returns it.
 * This mirrors Firestore error messaging for malformed fieldFilter clauses.
 *
 * @typeParam T - The expected type of the value.
 * @param argName - Name of the missing sub-field (e.g., `"op"`, `"value"`, `"fieldPath"`).
 * @param value - The value to check.
 * @returns The value when present.
 * @throws {GoogleError} {@link Status.INVALID_ARGUMENT} when the sub-field is missing.
 */
export declare function assertFieldArgument<T>(argName: string, value: T | null | undefined): T;
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