1 files changed, 192 insertions, 0 deletions
diff --git a/SoraTests/ViewDerivedDataTests.swift b/SoraTests/ViewDerivedDataTests.swift
new file mode 100644
index 0000000..6737265
--- /dev/null
+++ b/SoraTests/ViewDerivedDataTests.swift
@@ -0,0 +1,192 @@
+import Foundation
+import XCTest
+
+final class ViewDerivedDataTests: XCTestCase {
+  func testGenericListViewDerivedCollectionsAreReferencedOncePerRenderPass() throws {
+    let source = try loadSource(at: "Sora/Views/Generic/GenericListView.swift")
+    let normalizedSource = strippingCommentsAndStrings(from: source)
+
+    let filteredItemsUsages = referenceCount(
+      for: "filteredItems",
+      in: normalizedSource
+    )
+    let sortedFilteredItemsUsages = referenceCount(
+      for: "sortedFilteredItems",
+      in: normalizedSource
+    )
+
+    // swiftlint:disable:next prefer_nimble
+    XCTAssertLessThanOrEqual(
+      filteredItemsUsages,
+      1,
+      "filteredItems should be consumed once per dependency change."
+    )
+    // swiftlint:disable:next prefer_nimble
+    XCTAssertLessThanOrEqual(
+      sortedFilteredItemsUsages,
+      1,
+      "sortedFilteredItems should be consumed once per dependency change."
+    )
+  }
+
+  func testPostGridViewDerivedCollectionsAreReferencedOncePerRenderPass() throws {
+    let source = try loadSource(at: "Sora/Views/Post/Grid/PostGridView.swift")
+    let normalizedSource = strippingCommentsAndStrings(from: source)
+
+    let activePostsUsages = referenceCount(
+      for: "activePosts",
+      in: normalizedSource
+    )
+    let getColumnsDataUsages = invocationCount(
+      forFunction: "getColumnsData",
+      in: normalizedSource
+    )
+
+    // swiftlint:disable:next prefer_nimble
+    XCTAssertLessThanOrEqual(
+      activePostsUsages,
+      1,
+      "activePosts-derived data should be consumed once per dependency change."
+    )
+    // swiftlint:disable:next prefer_nimble
+    XCTAssertLessThanOrEqual(
+      getColumnsDataUsages,
+      1,
+      "getColumnsData should be invoked once per dependency change."
+    )
+  }
+
+  private func loadSource(at relativePath: String) throws -> String {
+    let currentFile = URL(fileURLWithPath: #filePath)
+    let repositoryRoot = currentFile.deletingLastPathComponent().deletingLastPathComponent()
+    let fileURL = repositoryRoot.appendingPathComponent(relativePath)
+
+    return try String(contentsOf: fileURL, encoding: .utf8)
+  }
+
+  // swiftlint:disable:next cyclomatic_complexity
+  private func strippingCommentsAndStrings(from source: String) -> String {
+    let characters = Array(source)
+    var result: [Character] = []
+    result.reserveCapacity(characters.count)
+
+    var currentOffset = 0
+    var inLineComment = false
+    var blockCommentDepth = 0
+    var inString = false
+    var isEscaped = false
+
+    while currentOffset < characters.count {
+      let current = characters[currentOffset]
+      let next: Character? = currentOffset + 1 < characters.count ? characters[currentOffset + 1] : nil
+
+      if inLineComment {
+        if current == "\n" {
+          inLineComment = false
+          result.append("\n")
+        } else {
+          result.append(" ")
+        }
+        currentOffset += 1
+        continue
+      }
+
+      if blockCommentDepth > 0 {
+        if current == "/", next == "*" {
+          blockCommentDepth += 1
+          result.append(" ")
+          result.append(" ")
+          currentOffset += 2
+          continue
+        }
+
+        if current == "*", next == "/" {
+          blockCommentDepth -= 1
+          result.append(" ")
+          result.append(" ")
+          currentOffset += 2
+          continue
+        }
+
+        result.append(current == "\n" ? "\n" : " ")
+        currentOffset += 1
+        continue
+      }
+
+      if inString {
+        if isEscaped {
+          isEscaped = false
+        } else if current == "\\" {
+          isEscaped = true
+        } else if current == "\"" {
+          inString = false
+        }
+
+        result.append(current == "\n" ? "\n" : " ")
+        currentOffset += 1
+        continue
+      }
+
+      if current == "/", next == "/" {
+        inLineComment = true
+        result.append(" ")
+        result.append(" ")
+        currentOffset += 2
+        continue
+      }
+
+      if current == "/", next == "*" {
+        blockCommentDepth = 1
+        result.append(" ")
+        result.append(" ")
+        currentOffset += 2
+        continue
+      }
+
+      if current == "\"" {
+        inString = true
+        result.append(" ")
+        currentOffset += 1
+        continue
+      }
+
+      result.append(current)
+      currentOffset += 1
+    }
+
+    return String(result)
+  }
+
+  private func referenceCount(for symbol: String, in source: String) -> Int {
+    let totalMatches = tokenCount(
+      matching: #"\b\#(symbol)\b"#,
+      in: source
+    )
+    let declarationMatches = tokenCount(
+      matching: #"\b(?:var|let)\s+\#(symbol)\b"#,
+      in: source
+    )
+
+    return max(0, totalMatches - declarationMatches)
+  }
+
+  private func invocationCount(forFunction name: String, in source: String) -> Int {
+    let totalMatches = tokenCount(
+      matching: #"\b\#(name)\s*\("#,
+      in: source
+    )
+    let declarationMatches = tokenCount(
+      matching: #"\bfunc\s+\#(name)\s*\("#,
+      in: source
+    )
+
+    return max(0, totalMatches - declarationMatches)
+  }
+
+  private func tokenCount(matching pattern: String, in source: String) -> Int {
+    guard let regex = try? NSRegularExpression(pattern: pattern) else { return 0 }
+    let range = NSRange(source.startIndex..<source.endIndex, in: source)
+
+    return regex.numberOfMatches(in: source, range: range)
+  }
+}