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Add assert and precondition (#213)
* Add `assert` and `precondition` Lightweight ways of writing assertions and preconditions in a testable fashion. * wip * wip * wip * Update Sources/Dependencies/DependencyValues/Assert.swift * wip * wip * wip * wip
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‎Dependencies.xcworkspace/xcshareddata/swiftpm/Package.resolved‎

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‎Package.resolved‎

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‎Sources/Dependencies/DependencyValues/Assert.swift‎

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extension DependencyValues {
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/// A dependency for handling assertions.
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///
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/// Useful as a controllable and testable substitute for Swift's `assert` function that calls
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/// `XCTFail` in tests instead of terminating the executable.
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///
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/// ```swift
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/// func operate(_ n: Int) {
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/// @Dependency(\.assert) var assert
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/// assert(n > 0, "Number must be greater than zero")
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/// // ...
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/// }
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/// ```
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///
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/// Tests can assert against this precondition using `XCTExpectFailure`:
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///
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/// ```swift
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/// XCTExpectFailure {
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/// operate(n)
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/// } issueMatcher: {
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/// $0.compactDescription = "Number must be greater than zero"
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/// }
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/// ```
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public var assert: any AssertionEffect {
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get { self[AssertKey.self] }
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set { self[AssertKey.self] = newValue }
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}
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/// A dependency for failing an assertion.
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///
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/// Equivalent to passing a `false` condition to ``DependencyValues/assert``.
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public var assertionFailure: any AssertionFailureEffect {
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AssertionFailure(base: self.assert)
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}
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/// A dependency for handling preconditions.
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///
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/// Useful as a controllable and testable substitute for Swift's `precondition` function that
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/// calls `XCTFail` in tests instead of terminating the executable.
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///
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/// ```swift
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/// func operate(_ n: Int) {
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/// @Dependency(\.precondition) var precondition
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/// precondition(n > 0, "Number must be greater than zero")
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/// // ...
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/// }
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/// ```
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///
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/// Tests can assert against this precondition using `XCTExpectFailure`:
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///
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/// ```swift
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/// XCTExpectFailure {
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/// operate(n)
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/// } issueMatcher: {
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/// $0.compactDescription = "Number must be greater than zero"
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/// }
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/// ```
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public var precondition: any AssertionEffect {
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get { self[PreconditionKey.self] }
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set { self[PreconditionKey.self] = newValue }
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}
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}
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/// A type for creating an assertion or precondition.
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///
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/// See ``DependencyValues/assert`` or ``DependencyValues/precondition`` for more information.
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public protocol AssertionEffect: Sendable {
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func callAsFunction(
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_ condition: @autoclosure () -> Bool,
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_ message: @autoclosure () -> String,
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file: StaticString,
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line: UInt
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)
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}
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extension AssertionEffect {
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@_disfavoredOverload
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@_transparent
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public func callAsFunction(
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_ condition: @autoclosure () -> Bool,
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_ message: @autoclosure () -> String = "",
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file: StaticString = #file,
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line: UInt = #line
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) {
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self.callAsFunction(condition(), message(), file: file, line: line)
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}
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}
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private struct LiveAssertionEffect: AssertionEffect {
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@_transparent
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func callAsFunction(
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_ condition: @autoclosure () -> Bool,
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_ message: @autoclosure () -> String,
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file: StaticString,
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line: UInt
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) {
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Swift.assert(condition(), message(), file: file, line: line)
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}
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}
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private struct LivePreconditionEffect: AssertionEffect {
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@_transparent
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func callAsFunction(
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_ condition: @autoclosure () -> Bool,
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_ message: @autoclosure () -> String,
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file: StaticString,
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line: UInt
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) {
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Swift.precondition(condition(), message(), file: file, line: line)
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}
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}
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private struct TestAssertionEffect: AssertionEffect {
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@_transparent
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func callAsFunction(
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_ condition: @autoclosure () -> Bool,
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_ message: @autoclosure () -> String,
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file: StaticString,
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line: UInt
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) {
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guard condition() else { return XCTFail(message(), file: file, line: line) }
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}
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}
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public protocol AssertionFailureEffect: Sendable {
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func callAsFunction(
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_ message: @autoclosure () -> String,
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file: StaticString,
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line: UInt
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)
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}
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extension AssertionFailureEffect {
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@_disfavoredOverload
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@_transparent
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public func callAsFunction(
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_ message: @autoclosure () -> String = "",
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file: StaticString = #file,
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line: UInt = #line
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) {
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self.callAsFunction(message(), file: file, line: line)
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}
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}
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private struct AssertionFailure: AssertionFailureEffect {
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let base: any AssertionEffect
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@_transparent
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func callAsFunction(
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_ message: @autoclosure () -> String,
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file: StaticString,
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line: UInt
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) {
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self.base(false, message(), file: file, line: line)
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}
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}
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private enum AssertKey: DependencyKey {
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public static let liveValue: any AssertionEffect = LiveAssertionEffect()
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public static let testValue: any AssertionEffect = TestAssertionEffect()
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}
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private enum PreconditionKey: DependencyKey {
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public static let liveValue: any AssertionEffect = LivePreconditionEffect()
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public static let testValue: any AssertionEffect = TestAssertionEffect()
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}
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/// An ``AssertionEffect`` that invokes the given closure.
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public struct AnyAssertionEffect: AssertionEffect {
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private let assert: @Sendable (
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_ condition: @autoclosure () -> Bool,
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_ message: @autoclosure () -> String,
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_ file: StaticString,
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_ line: UInt
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) -> Void
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public init(
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_ assert: @escaping @Sendable (
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_ condition: @autoclosure () -> Bool,
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_ message: @autoclosure () -> String,
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_ file: StaticString,
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_ line: UInt
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) -> Void
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) {
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self.assert = assert
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}
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public func callAsFunction(
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_ condition: @autoclosure () -> Bool,
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_ message: @autoclosure () -> String,
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file: StaticString,
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line: UInt
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) {
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self.assert(condition(), message(), file, line)
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}
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}

‎Sources/Dependencies/Documentation.docc/Extensions/DependencyValues.md‎

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### Creating and accessing values
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- ``init()``
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- ``subscript(_:_:_:_:)``
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- ``subscript(key:file:function:line:)
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### Overriding values
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### Dependency values
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- ``assert``
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- ``assertionFailure``
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- ``calendar``
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- ``context``
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- ``continuousClock``
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- ``mainQueue``
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- ``mainRunLoop``
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- ``openURL``
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- ``precondition``
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- ``suspendingClock``
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- ``timeZone``
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- ``urlSession``

‎Sources/Dependencies/Documentation.docc/Extensions/DependencyValuesAssert.md‎

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# ``Dependencies/DependencyValues/assert``
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## Topics
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### Dependency values
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- ``AssertionEffect``
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- ``AssertionFailureEffect``
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### Custom assertions
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- ``AnyAssertionEffect``

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