perl: expand and refactor tests

This brings coverage of `Language::Perl::Shebang` to 100%.

Library/Homebrew/test/language/perl/shebang_spec.rb

@@ -5,17 +5,30 @@ require "utils/shebang"
 
 describe Language::Perl::Shebang do
   let(:file) { Tempfile.new("perl-shebang") }
-  let(:perl_f) do
-    formula "perl" do
+  let(:f) do
+    f = {}
+
+    f[:perl] = formula "perl" do
       url "https://brew.sh/perl-1.0.tgz"
     end
-  end
-  let(:f) do
-    formula "foo" do
+
+    f[:depends_on] = formula "foo" do
+      url "https://brew.sh/foo-1.0.tgz"
+
+      depends_on "perl"
+    end
+
+    f[:uses_from_macos] = formula "foo" do
       url "https://brew.sh/foo-1.0.tgz"
 
       uses_from_macos "perl"
     end
+
+    f[:no_deps] = formula "foo" do
+      url "https://brew.sh/foo-1.0.tgz"
+    end
+
+    f
   end
 
   before do
@@ -31,10 +44,23 @@ describe Language::Perl::Shebang do
   after { file.unlink }
 
   describe "#detected_perl_shebang" do
-    it "can be used to replace Perl shebangs" do
+    it "can be used to replace Perl shebangs when depends_on \"perl\" is used" do
       allow(Formulary).to receive(:factory)
-      allow(Formulary).to receive(:factory).with(perl_f.name).and_return(perl_f)
-      Utils::Shebang.rewrite_shebang described_class.detected_perl_shebang(f), file.path
+      allow(Formulary).to receive(:factory).with(f[:perl].name).and_return(f[:perl])
+      Utils::Shebang.rewrite_shebang described_class.detected_perl_shebang(f[:depends_on]), file.path
+
+      expect(File.read(file)).to eq <<~EOS
+        #!#{HOMEBREW_PREFIX}/opt/perl/bin/perl
+        a
+        b
+        c
+      EOS
+    end
+
+    it "can be used to replace Perl shebangs when uses_from_macos \"perl\" is used" do
+      allow(Formulary).to receive(:factory)
+      allow(Formulary).to receive(:factory).with(f[:perl].name).and_return(f[:perl])
+      Utils::Shebang.rewrite_shebang described_class.detected_perl_shebang(f[:uses_from_macos]), file.path
 
       expected_shebang = if OS.mac?
         "/usr/bin/perl#{MacOS.preferred_perl_version}"
@@ -49,5 +75,10 @@ describe Language::Perl::Shebang do
         c
       EOS
     end
+
+    it "errors if formula doesn't depend on perl" do
+      expect { Utils::Shebang.rewrite_shebang described_class.detected_perl_shebang(f[:no_deps]), file.path }
+        .to raise_error(ShebangDetectionError, "Cannot detect Perl shebang: formula does not depend on Perl.")
+    end
   end
 end