refactor(loader): Throw when template not found

Tests/StencilTests/LoaderSpec.swift

@@ -0,0 +1,31 @@
+import Spectre
+import Stencil
+import PathKit
+
+
+func testTemplateLoader() {
+  describe("FileSystemLoader") {
+    let path = Path(#file) + ".."  + "fixtures"
+    let loader = FileSystemLoader(paths: [path])
+
+    $0.it("errors when a template cannot be found") {
+      try expect(try loader.loadTemplate(name: "unknown.html")).toThrow()
+    }
+
+    $0.it("errors when an array of templates cannot be found") {
+      try expect(try loader.loadTemplate(names: ["unknown.html", "unknown2.html"])).toThrow()
+    }
+
+    $0.it("can load a template from a file") {
+      _ = try loader.loadTemplate(name: "test.html")
+    }
+
+    $0.it("errors when loading absolute file outside of the selected path") {
+      try expect(try loader.loadTemplate(name: "/etc/hosts")).toThrow()
+    }
+
+    $0.it("errors when loading relative file outside of the selected path") {
+      try expect(try loader.loadTemplate(name: "../LoaderSpec.swift")).toThrow()
+    }
+  }
+}