Add tests for `CaskUnreadableError.

Library/Homebrew/test/cask/cask_loader/from__path_loader_spec.rb

@@ -0,0 +1,35 @@
+describe Hbc::CaskLoader::FromPathLoader do
+  describe "#load" do
+    context "when the file does not contain a cask" do
+      let(:path) {
+        (mktmpdir/"cask.rb").tap do |path|
+          path.write <<~RUBY
+            true
+          RUBY
+        end
+      }
+
+      it "raises an error" do
+        expect {
+          described_class.new(path).load
+        }.to raise_error(Hbc::CaskUnreadableError, /does not contain a cask/)
+      end
+    end
+
+    context "when the file calls a non-existent method" do
+      let(:path) {
+        (mktmpdir/"cask.rb").tap do |path|
+          path.write <<~RUBY
+            this_method_does_not_exist
+          RUBY
+        end
+      }
+
+      it "raises an error" do
+        expect {
+          described_class.new(path).load
+        }.to raise_error(Hbc::CaskUnreadableError, /undefined local variable or method/)
+      end
+    end
+  end
+end

Library/Homebrew/test/cask/dsl_spec.rb

@@ -46,7 +46,7 @@ describe Hbc::DSL, :cask do
       let(:token) { "invalid/invalid-header-format" }
 
       it "raises an error" do
-        expect { cask }.to raise_error(SyntaxError)
+        expect { cask }.to raise_error(Hbc::CaskUnreadableError)
       end
     end