[InteropTests] Create test framework

Sources/InteroperabilityTests/AssertionFailure.swift

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+/*
+ * Copyright 2024, gRPC 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.
+ */
+
+/// Failure assertion for interoperability testing.
+///
+/// This is required because the tests must be able to run without XCTest.
+public struct AssertionFailure: Error {
+  public var message: String
+  public var file: String
+  public var line: Int
+}
+
+/// Asserts that the value of an expression is `true`.
+public func assertTrue(
+  _ expression: @autoclosure () throws -> Bool,
+  _ message: String = "The statement is not true.",
+  file: String = #fileID,
+  line: Int = #line
+) throws {
+  guard try expression() else {
+    throw AssertionFailure(message: message, file: file, line: line)
+  }
+}