test: Cover the remaining content-coding branches

Fills the gaps JaCoCo flagged: repeated codings in one Accept-Encoding
header, weight parameters mixed with others, a valueless parameter, 304
responses, an unparsable hand-set Content-Length, and streams whose
handler supplied its own Content-Type or Content-Encoding.

Branch coverage on AcceptEncodingHeader goes 70% to 93% and on
ResponseRenderer 83% to 87%, keeping the new code clear of the Sonar
new-code gate.

Author: thced

src/test/java/com/retailsvc/http/internal/AcceptEncodingHeaderTest.java

@@ -91,4 +91,26 @@ void malformedQValueIsTreatedAsAccepted() {
   void emptyTokensAreIgnored() {
     assertThat(AcceptEncodingHeader.acceptsGzip("deflate,,gzip")).isTrue();
   }
+
+  @Test
+  void repeatedGzipTokensTakeThePositiveWeight() {
+    assertThat(AcceptEncodingHeader.acceptsGzip("gzip;q=0, gzip")).isTrue();
+    assertThat(AcceptEncodingHeader.acceptsGzip("gzip, x-gzip;q=0")).isTrue();
+  }
+
+  @Test
+  void repeatedWildcardsTakeThePositiveWeight() {
+    assertThat(AcceptEncodingHeader.acceptsGzip("*;q=0, *")).isTrue();
+  }
+
+  @Test
+  void parametersOtherThanWeightAreIgnored() {
+    assertThat(AcceptEncodingHeader.acceptsGzip("gzip;level=9")).isTrue();
+    assertThat(AcceptEncodingHeader.acceptsGzip("gzip;level=9;q=0")).isFalse();
+  }
+
+  @Test
+  void valuelessParameterIsIgnored() {
+    assertThat(AcceptEncodingHeader.acceptsGzip("gzip;q")).isTrue();
+  }
 }

src/test/java/com/retailsvc/http/internal/ResponseRendererTest.java

@@ -1,5 +1,6 @@
 package com.retailsvc.http.internal;
 
+import static java.net.HttpURLConnection.HTTP_NOT_MODIFIED;
 import static java.net.HttpURLConnection.HTTP_NO_CONTENT;
 import static java.net.HttpURLConnection.HTTP_OK;
 import static java.nio.charset.StandardCharsets.UTF_8;
@@ -346,6 +347,56 @@ void keepsContentLengthOnNullBodyBelowThreshold() throws IOException {
     assertThat(responseHeaders.getFirst("Content-Length")).isEqualTo("12");
   }
 
+  @Test
+  void neverCompressesNotModifiedResponses() throws IOException {
+    acceptsGzip();
+
+    renderer.render(exchange, Response.bytes(HTTP_NOT_MODIFIED, largeText(), JSON));
+
+    assertThat(responseHeaders.getFirst(CONTENT_ENCODING)).isNull();
+  }
+
+  @Test
+  void keepsContentLengthOnNullBodyWhenUnparsable() throws IOException {
+    acceptsGzip();
+
+    renderer.render(
+        exchange,
+        Response.status(HTTP_OK)
+            .withContentType(TEXT)
+            .withHeader("Content-Length", "not-a-number"));
+
+    assertThat(responseHeaders.getFirst("Content-Length")).isEqualTo("not-a-number");
+  }
+
+  @Test
+  void keepsHandlerSuppliedContentTypeOnStreams() throws IOException {
+    acceptsGzip();
+    byte[] payload = largeText();
+
+    renderer.render(
+        exchange,
+        Response.stream(HTTP_OK, TEXT, out -> out.write(payload))
+            .withHeader("Content-Type", "text/csv"));
+
+    assertThat(responseHeaders.get("Content-Type")).containsExactly("text/csv");
+    assertThat(gunzip(sink.toByteArray())).isEqualTo(payload);
+  }
+
+  @Test
+  void skipsCompressionOnStreamWhenHandlerAlreadySetContentEncoding() throws IOException {
+    acceptsGzip();
+    byte[] payload = largeText();
+
+    renderer.render(
+        exchange,
+        Response.stream(HTTP_OK, TEXT, out -> out.write(payload))
+            .withHeader(CONTENT_ENCODING, "br"));
+
+    assertThat(responseHeaders.get(CONTENT_ENCODING)).containsExactly("br");
+    assertThat(sink.toByteArray()).isEqualTo(payload);
+  }
+
   private void acceptsGzip() {
     requestHeaders.add("Accept-Encoding", "gzip, deflate, br");
   }