Add tests for coverage subcommand

Author: mattt

Tests/EndToEndTests/CoverageSubcommandTests.swift

@@ -0,0 +1,47 @@
+import XCTest
+
+final class CoverageSubcommandTests: XCTestCase {
+    func testStandardOutput() throws {
+        let command = Bundle.productsDirectory.appendingPathComponent("swift-doc")
+
+        let outputDirectory = try temporaryDirectory()
+        defer { try? FileManager.default.removeItem(at: outputDirectory) }
+
+        try Process.run(command: command,
+                        arguments: [
+                            "coverage",
+                            "Sources"
+                        ]
+        ) { result in
+            XCTAssertEqual(result.terminationStatus, EXIT_SUCCESS)
+            XCTAssertEqual(result.output?.starts(with: "Total"), true)
+            XCTAssertEqual(result.error, "")
+        }
+    }
+
+    func testFileOutput() throws {
+        let command = Bundle.productsDirectory.appendingPathComponent("swift-doc")
+        
+        let outputDirectory = try temporaryDirectory()
+        let outputFile = outputDirectory.appendingPathComponent("report.json")
+        defer { try? FileManager.default.removeItem(at: outputDirectory) }
+
+        try Process.run(command: command,
+                        arguments: [
+                            "coverage",
+                            "--output", outputFile.path,
+                            "Sources"
+                        ]
+        ) { result in
+            XCTAssertEqual(result.terminationStatus, EXIT_SUCCESS)
+            XCTAssertEqual(result.output, "")
+            XCTAssertEqual(result.error, "")
+
+            do {
+                let data = try Data(contentsOf: outputFile)
+                let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String: Any]
+                XCTAssertEqual(json?["type"] as? String, "org.dcov.report.json.export")
+            }
+        }
+    }
+}

Tests/EndToEndTests/GenerateSubcommandTests.swift

@@ -1,12 +1,12 @@
-import class Foundation.Bundle
 import XCTest
 
 final class GenerateSubcommandTests: XCTestCase {
     func testCommonMark() throws {
         let command = Bundle.productsDirectory.appendingPathComponent("swift-doc")
-        let outputDirectory = try temporaryDirectory()
 
+        let outputDirectory = try temporaryDirectory()
         defer { try? FileManager.default.removeItem(at: outputDirectory) }
+        
         try Process.run(command: command,
                         arguments: [
                             "generate",