refactor(loader): Throw when template not found

Tests/StencilTests/IncludeSpec.swift

@@ -45,7 +45,7 @@ func testInclude() {
         do {
           _ = try node.render(Context(dictionary: ["loader": loader]))
         } catch {
-          try expect("\(error)".hasPrefix("'unknown.html' template not found")).to.beTrue()
+          try expect("\(error)".hasPrefix("Template named `unknown.html` does not exist in loader")).to.beTrue()
         }
       }
 

Tests/StencilTests/InheritenceSpec.swift

@@ -11,13 +11,13 @@ func testInheritence() {
     $0.it("can inherit from another template") {
       let context = Context(dictionary: ["loader": loader])
       let template = try loader.loadTemplate(name: "child.html")
-      try expect(try template?.render(context)) == "Header\nChild"
+      try expect(try template.render(context)) == "Header\nChild"
     }
 
     $0.it("can inherit from another template inheriting from another template") {
       let context = Context(dictionary: ["loader": loader])
       let template = try loader.loadTemplate(name: "child-child.html")
-      try expect(try template?.render(context)) == "Child Child Header\nChild"
+      try expect(try template.render(context)) == "Child Child Header\nChild"
     }
   }
 }

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()
+    }
+  }
+}