From 85e77dc3a78f524f6721d4f21e8924aee2ebd4ad Mon Sep 17 00:00:00 2001
From: Mark Eschbach <meschbach@gmail.com>
Date: Tue, 16 Apr 2019 11:19:24 -0700
Subject: [PATCH] vfs: Ensure file not found message is intelligable

---
 tests/vfs-tests.js | 14 ++++++++++++++
 vfs.js             | 11 ++++++++---
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/tests/vfs-tests.js b/tests/vfs-tests.js
index 16891fb..98b558d 100644
--- a/tests/vfs-tests.js
+++ b/tests/vfs-tests.js
@@ -17,6 +17,20 @@ function abstractVFSBehavior( VFS, name ) {
 				const sut = new VFS();
 				expect(await sut.exists("nonexistent-file")).to.eq(false);
 			});
+
+			it("raises a reasonable error the file does not exist", async function () {
+				const exampleFileName = "non-existent-file";
+				let raised = false;
+				try {
+					const sut = new VFS();
+					await sut.asBytes(exampleFileName);
+				}catch(e){
+					raised = true;
+					expect(e.message).to.include(exampleFileName);
+				}finally {
+					expect(raised).to.eq(true);
+				}
+			})
 		});
 
 		describe("When creating a file as bytes", function(){
diff --git a/vfs.js b/vfs.js
index 3af453c..29dce9e 100644
--- a/vfs.js
+++ b/vfs.js
@@ -20,6 +20,12 @@ class InMemoryVFS {
 		return !!this.files[file];
 	}
 
+	async _expectFile( file ){
+		if( !this.files[file]){
+			throw new Error("No such file " + file);
+		}
+	}
+
 	async unlink( file ){
 		if( this.files[file] ){
 			delete this.files[file];
@@ -27,13 +33,12 @@ class InMemoryVFS {
 	}
 
 	async createReadableStream( file ){
-		if( !(await this.exists(file)) ){
-			throw new Error("No such file "+ file);
-		}
+		await this._expectFile(file);
 		return new MemoryReadable(this.files[file]);
 	}
 
 	async asBytes( file ){
+		await this._expectFile(file);
 		return Buffer.from(this.files[file]);
 	}