Add a test for WARNINGS.md (#660)

BUILD.bazel

@@ -6,6 +6,12 @@ config_setting(
     values = {"cpu": "x64_windows"},
 )
 
+filegroup(
+    name = "warnings",
+    srcs = ["WARNINGS.md"],
+    visibility = ["//warn:__pkg__"]
+)
+
 test_suite(
     name = "tests",
     tests = [
@@ -18,6 +24,7 @@ test_suite(
         "//extra_actions_base_proto:extra_actions_base.gen.pb.go_checkshtest",
         "//lang:tables.gen.go_checkshtest",
         "//tables:go_default_test",
+        "//warn:go_default_test",
         "//wspace:go_default_test",
     ],
 )

warn/BUILD.bazel

@@ -25,9 +25,10 @@ go_library(
 )
 
 go_test(
-    name = "warn_test",
+    name = "go_default_test",
     size = "small",
     srcs = [
+        "documentation_test.go",
         "types_test.go",
         "warn_bazel_api_test.go",
         "warn_bazel_operation_test.go",
@@ -40,6 +41,9 @@ go_test(
         "warn_test.go",
     ],
     embed = [":go_default_library"],
+    data = [
+        "//:warnings",
+    ],
     deps = [
         "//testutils",
     ],

warn/documentation_test.go

@@ -0,0 +1,37 @@
+package warn
+
+import (
+	"fmt"
+	"io/ioutil"
+	"strings"
+	"testing"
+
+	"github.com/bazelbuild/buildtools/testutils"
+)
+
+func TestWarningsDocumentation(t *testing.T) {
+	files, chdir := testutils.FindTests(t, "", "WARNINGS.md")
+	defer chdir()
+
+	if len(files) != 1 {
+		t.Fatalf("Expected to find exactly one WARNINGS.md file, got %d instead", len(files))
+	}
+	data, err := ioutil.ReadFile(files[0])
+	if err != nil {
+		t.Fatal(err)
+		return
+	}
+
+	contents := string(data)
+	for _, warning := range AllWarnings {
+		link := fmt.Sprintf("  * [%s](#%s)", warning, warning)
+		if !strings.Contains(contents, link) {
+			t.Errorf("No link (%q) found for the warning %q in WARNINGS.md, is it documented?", link, warning)
+		}
+
+		anchor := fmt.Sprintf(`<a name="%s"></a>`, warning)
+		if !strings.Contains(contents, anchor) {
+			t.Errorf("No anchor (%q) found for the warning %q in WARNINGS.md, is it documented?", anchor, warning)
+		}
+	}
+}