fix(fmt): --check was broken for CSS, YAML and HTML (#25848)

`deno fmt --check` was broken for CSS, YAML and HTML files.

Before this PR, formatting any of these file types would return a
string, even though the contract in `cli/tools/fmt.rs` is to only return a
string if the formatting changed. This causes wrong flagging of these files
as being badly formatted even though diffs showed nothing (because
they were in fact formatted properly).

Closes https://github.com/denoland/deno/issues/25840

6 files changed, 48 insertions, 7 deletions

diff --git a/tests/specs/fmt/css/__test__.jsonc b/tests/specs/fmt/css/__test__.jsonc
index e58818fbe..a3ded6d43 100644
--- a/tests/specs/fmt/css/__test__.jsonc
+++ b/tests/specs/fmt/css/__test__.jsonc
@@ -1,5 +1,13 @@
 {
   "tempDir": true,
-  "args": "fmt",
-  "output": "[WILDLINE]badly_formatted.css\nChecked 1 file\n"
+  "tests": {
+    "badly_formatted": {
+      "args": "fmt badly_formatted.css",
+      "output": "[WILDLINE]badly_formatted.css\nChecked 1 file\n"
+    },
+    "well_formatted": {
+      "args": "fmt --check well_formatted.css",
+      "output": "Checked 1 file\n"
+    }
+  }
 }
diff --git a/tests/specs/fmt/css/well_formatted.css b/tests/specs/fmt/css/well_formatted.css
new file mode 100644
index 000000000..1653551f4
--- /dev/null
+++ b/tests/specs/fmt/css/well_formatted.css
@@ -0,0 +1,3 @@
+#app > .btn {
+  color: #000;
+}
diff --git a/tests/specs/fmt/html/__test__.jsonc b/tests/specs/fmt/html/__test__.jsonc
index cec29d1b3..7f3169423 100644
--- a/tests/specs/fmt/html/__test__.jsonc
+++ b/tests/specs/fmt/html/__test__.jsonc
@@ -1,5 +1,13 @@
 {
   "tempDir": true,
-  "args": "fmt --unstable-html",
-  "output": "[WILDLINE]badly_formatted.html\nChecked 1 file\n"
+  "tests": {
+    "badly_formatted": {
+      "args": "fmt badly_formatted.html",
+      "output": "[WILDLINE]badly_formatted.html\nChecked 1 file\n"
+    },
+    "well_formatted": {
+      "args": "fmt --check well_formatted.html",
+      "output": "Checked 1 file\n"
+    }
+  }
 }
diff --git a/tests/specs/fmt/html/well_formatted.html b/tests/specs/fmt/html/well_formatted.html
new file mode 100644
index 000000000..c0c06cd9b
--- /dev/null
+++ b/tests/specs/fmt/html/well_formatted.html
@@ -0,0 +1,11 @@
+<div class="container">content</div>
+
+<script>
+  let counter = 0;
+</script>
+
+<style>
+  .container {
+    padding: 8px;
+  }
+</style>
diff --git a/tests/specs/fmt/yaml/__test__.jsonc b/tests/specs/fmt/yaml/__test__.jsonc
index 3cef276b8..499b4144b 100644
--- a/tests/specs/fmt/yaml/__test__.jsonc
+++ b/tests/specs/fmt/yaml/__test__.jsonc
@@ -1,5 +1,13 @@
 {
   "tempDir": true,
-  "args": "fmt",
-  "output": "[WILDLINE]badly_formatted.yml\nChecked 1 file\n"
-}
\ No newline at end of file
+  "tests": {
+    "badly_formatted": {
+      "args": "fmt badly_formatted.yml",
+      "output": "[WILDLINE]badly_formatted.yml\nChecked 1 file\n"
+    },
+    "well_formatted": {
+      "args": "fmt --check well_formatted.yml",
+      "output": "Checked 1 file\n"
+    }
+  }
+}
diff --git a/tests/specs/fmt/yaml/well_formatted.yml b/tests/specs/fmt/yaml/well_formatted.yml
new file mode 100644
index 000000000..016e0b951
--- /dev/null
+++ b/tests/specs/fmt/yaml/well_formatted.yml
@@ -0,0 +1,3 @@
+- Test
+- Test
+- Test