Add unit tests for everything that doesn't result in printErrorAndExit.

As verified by the wonderful new code coverage feature of Xcode.

SwiftShellTests/Context_Tests.swift

@@ -20,5 +20,6 @@ class Context_Tests: XCTestCase {
 
 		XCTAssertEqual( main.currentdirectory, "/private/tmp" )
 		XCTAssertEqual( main.$("/bin/pwd"), "/tmp" )
+		XCTAssertEqual( main.currentdirectory, NSFileManager.defaultManager().currentDirectoryPath )
 	}
 }

SwiftShellTests/FileHandle_Tests.swift

@@ -11,5 +11,30 @@ import XCTest
 
 class FileHandle_Tests: XCTestCase {
 
+	func testWriteAndReadSome () {
+		let pipe = NSPipe()
+		let writer = pipe.fileHandleForWriting
+		let reader = pipe.fileHandleForReading
 
+		writer.write("line1")
+		XCTAssertEqual(reader.readSome(), "line1")
+		writer.write("line2")
+		XCTAssertEqual(reader.readSome(), "line2")
+
+		writer.closeFile()
+		XCTAssertNil(reader.readSome())
+		XCTAssertNil(reader.readSome(), "Performing readSome() repeatedly on closed filehandle should return empty string.")
+		XCTAssertEqual(reader.read(), "")
+	}
+
+	func testWritelnAndRead () {
+		let pipe = NSPipe()
+		let writer = pipe.fileHandleForWriting
+		let reader = pipe.fileHandleForReading
+
+		writer.writeln("line1")
+		writer.closeFile()
+		XCTAssertEqual(reader.read(), "line1\n")
+		XCTAssertEqual(reader.read(), "", "Performing read() repeatedly on closed filehandle should return empty string.")
+	}
 }