Initial Visual Studio Code unit tests

As promised in #1439 this is an initial attempt at unit testing the
VSCode extension. There are two separate parts to this: getting the test
framework working and unit testing the code in #1439.

The test framework nearly intact from the VSCode extension generator.
The main thing missing was `test/index.ts` which acts as an entry point
for Mocha. This was simply copied back in. I also needed to open the
test VSCode instance inside a workspace as our file URI generation
depends on a workspace being open.

There are two ways to run the test framework:

1. Opening the extension's source in VSCode, pressing F5 and selecting
   the "Extensions Test" debug target.

2. Closing all copies of VSCode and running `npm test`. This is started
   from the command line but actually opens a temporary VSCode window to
   host the tests.

This doesn't attempt to wire this up to CI. That requires running a
headless X11 server which is a bit daunting. I'll assess the difficulty
of that in a follow-up branch. This PR is at least helpful for local
development without having to induce errors on a Rust project.

For the actual tests this uses snapshots of `rustc` output from a real
Rust project captured from the command line. Except for extracting the
`message` object and reformatting they're copied verbatim into fixture
JSON files.

Only four different types of diagnostics are tested but they represent
the main combinations of code actions and related information possible.
They can be considered the happy path tests; as we encounter
corner-cases we can introduce new tests fixtures.

1 files changed, 164 insertions, 0 deletions

diff --git a/editors/code/src/test/vscode_diagnostics.test.ts b/editors/code/src/test/vscode_diagnostics.test.ts
new file mode 100644
index 000000000..ca4345626
--- /dev/null
+++ b/editors/code/src/test/vscode_diagnostics.test.ts
@@ -0,0 +1,164 @@
+import * as assert from 'assert';
+import * as vscode from 'vscode';
+
+import {
+    areCodeActionsEqual,
+    areDiagnosticsEqual
+} from '../utils/vscode_diagnostics';
+
+const uri = vscode.Uri.file('/file/1');
+
+const range1 = new vscode.Range(
+    new vscode.Position(1, 2),
+    new vscode.Position(3, 4)
+);
+
+const range2 = new vscode.Range(
+    new vscode.Position(5, 6),
+    new vscode.Position(7, 8)
+);
+
+describe('areDiagnosticsEqual', () => {
+    it('should treat identical diagnostics as equal', () => {
+        const diagnostic1 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        const diagnostic2 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        assert(areDiagnosticsEqual(diagnostic1, diagnostic2));
+    });
+
+    it('should treat diagnostics with different ranges as inequal', () => {
+        const diagnostic1 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        const diagnostic2 = new vscode.Diagnostic(
+            range2,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        assert(!areDiagnosticsEqual(diagnostic1, diagnostic2));
+    });
+
+    it('should treat diagnostics with different messages as inequal', () => {
+        const diagnostic1 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        const diagnostic2 = new vscode.Diagnostic(
+            range1,
+            'Goodbye!, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        assert(!areDiagnosticsEqual(diagnostic1, diagnostic2));
+    });
+
+    it('should treat diagnostics with different severities as inequal', () => {
+        const diagnostic1 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Warning
+        );
+
+        const diagnostic2 = new vscode.Diagnostic(
+            range1,
+            'Hello, world!',
+            vscode.DiagnosticSeverity.Error
+        );
+
+        assert(!areDiagnosticsEqual(diagnostic1, diagnostic2));
+    });
+});
+
+describe('areCodeActionsEqual', () => {
+    it('should treat identical actions as equal', () => {
+        const codeAction1 = new vscode.CodeAction(
+            'Fix me!',
+            vscode.CodeActionKind.QuickFix
+        );
+
+        const codeAction2 = new vscode.CodeAction(
+            'Fix me!',
+            vscode.CodeActionKind.QuickFix
+        );
+
+        const edit = new vscode.WorkspaceEdit();
+        edit.replace(uri, range1, 'Replace with this');
+        codeAction1.edit = edit;
+        codeAction2.edit = edit;
+
+        assert(areCodeActionsEqual(codeAction1, codeAction2));
+    });
+
+    it('should treat actions with different types as inequal', () => {
+        const codeAction1 = new vscode.CodeAction(
+            'Fix me!',
+            vscode.CodeActionKind.Refactor
+        );
+
+        const codeAction2 = new vscode.CodeAction(
+            'Fix me!',
+            vscode.CodeActionKind.QuickFix
+        );
+
+        const edit = new vscode.WorkspaceEdit();
+        edit.replace(uri, range1, 'Replace with this');
+        codeAction1.edit = edit;
+        codeAction2.edit = edit;
+
+        assert(!areCodeActionsEqual(codeAction1, codeAction2));
+    });
+
+    it('should treat actions with different titles as inequal', () => {
+        const codeAction1 = new vscode.CodeAction(
+            'Fix me!',
+            vscode.CodeActionKind.Refactor
+        );
+
+        const codeAction2 = new vscode.CodeAction(
+            'Do something different!',
+            vscode.CodeActionKind.Refactor
+        );
+
+        const edit = new vscode.WorkspaceEdit();
+        edit.replace(uri, range1, 'Replace with this');
+        codeAction1.edit = edit;
+        codeAction2.edit = edit;
+
+        assert(!areCodeActionsEqual(codeAction1, codeAction2));
+    });
+
+    it('should treat actions with different edits as inequal', () => {
+        const codeAction1 = new vscode.CodeAction(
+            'Fix me!',
+            vscode.CodeActionKind.Refactor
+        );
+        const edit1 = new vscode.WorkspaceEdit();
+        edit1.replace(uri, range1, 'Replace with this');
+        codeAction1.edit = edit1;
+
+        const codeAction2 = new vscode.CodeAction(
+            'Fix me!',
+            vscode.CodeActionKind.Refactor
+        );
+        const edit2 = new vscode.WorkspaceEdit();
+        edit2.replace(uri, range1, 'Replace with this other thing');
+        codeAction2.edit = edit2;
+
+        assert(!areCodeActionsEqual(codeAction1, codeAction2));
+    });
+});