Print verbose output in HRX format (#95)

Eventually we want to print this in diff format (see #27), but there's
not an up-to-date diff library in Dart at the moment so this is a
stop-gap measure for better output.

lib/src/runner.dart

@@ -106,12 +106,16 @@ class MigratorRunner extends CommandRunner<Map<Uri, String>> {
 
     if (argResults['dry-run']) {
       print('Dry run. Logging migrated files instead of overwriting...\n');
+
       for (var url in migrated.keys) {
-        print(p.prettyUri(url));
         if (argResults['verbose']) {
-          print('=' * 80);
+          // This isn't *strictly* HRX format, since it can produce absolute
+          // URLs rather than those that are relative to the HRX root, but we
+          // just need it to be readable, not to interoperate with other tools.
+          print('<===> ${p.prettyUri(url)}');
           print(migrated[url]);
-          print('-' * 80);
+        } else {
+          print(p.prettyUri(url));
         }
       }
     } else {

test/cli_dart_test.dart

@@ -29,6 +29,99 @@ void main() {
     await migrator.shouldExit(0);
   });
 
+  group("with --dry-run", () {
+    test("prints the name of a file that would be migrated", () async {
+      await d.file("test.scss", "a {b: abs(-1)}").create();
+
+      var migrator = await runMigrator(["--dry-run", "module", "test.scss"]);
+      expect(
+          migrator.stdout,
+          emitsInOrder([
+            "Dry run. Logging migrated files instead of overwriting...",
+            "",
+            "test.scss",
+            emitsDone
+          ]));
+      await migrator.shouldExit(0);
+    });
+
+    test("doesn't print the name of a file that doesn't need to be migrated",
+        () async {
+      await d.file("test.scss", "a {b: abs(-1)}").create();
+      await d.file("other.scss", "a {b: c}").create();
+
+      var migrator =
+          await runMigrator(["--dry-run", "module", "test.scss", "other.scss"]);
+      expect(
+          migrator.stdout,
+          emitsInOrder([
+            "Dry run. Logging migrated files instead of overwriting...",
+            "",
+            "test.scss",
+            emitsDone
+          ]));
+      await migrator.shouldExit(0);
+    });
+
+    test("doesn't print the name of imported files without --migrate-deps",
+        () async {
+      await d.file("test.scss", "@import 'other'").create();
+      await d.file("_other.scss", "a {b: abs(-1)}").create();
+
+      var migrator = await runMigrator(["--dry-run", "module", "test.scss"]);
+      expect(
+          migrator.stdout,
+          emitsInOrder([
+            "Dry run. Logging migrated files instead of overwriting...",
+            "",
+            "test.scss",
+            emitsDone
+          ]));
+      await migrator.shouldExit(0);
+    });
+
+    test("prints the name of imported files with --migrate-deps", () async {
+      await d.file("test.scss", "@import 'other'").create();
+      await d.file("_other.scss", "a {b: abs(-1)}").create();
+
+      var migrator = await runMigrator(
+          ["--dry-run", "--migrate-deps", "module", "test.scss"]);
+      expect(
+          migrator.stdout,
+          emitsInOrder([
+            "Dry run. Logging migrated files instead of overwriting...",
+            "",
+            emitsInAnyOrder(["test.scss", "_other.scss"]),
+            emitsDone
+          ]));
+      await migrator.shouldExit(0);
+    });
+
+    test("prints the contents of migrated files with --verbose", () async {
+      await d.file("test.scss", "@import 'other'").create();
+      await d.file("_other.scss", "a {b: abs(-1)}").create();
+
+      var migrator = await runMigrator(
+          ["--dry-run", "--migrate-deps", "--verbose", "module", "test.scss"]);
+      expect(
+          migrator.stdout,
+          emitsInOrder([
+            "Dry run. Logging migrated files instead of overwriting...",
+            "",
+            emitsInAnyOrder([
+              emitsInOrder(["<===> test.scss", "@use 'other'"]),
+              emitsInOrder([
+                "<===> _other.scss",
+                '@use "sass:math";',
+                "a {b: math.abs(-1)}"
+              ]),
+            ]),
+            emitsDone
+          ]));
+      await migrator.shouldExit(0);
+    });
+  });
+
   group("gracefully handles", () {
     test("an unknown command", () async {
       var migrator = await runMigrator(["asdf"]);