Add unit tests of the different flush kinds

src/mem.rs

@@ -603,7 +603,6 @@ mod tests {
     use crate::write;
     use crate::{Compression, Decompress, FlushDecompress};
 
-    #[cfg(feature = "any_zlib")]
     use crate::{Compress, FlushCompress};
 
     #[test]
@@ -783,4 +782,66 @@ mod tests {
 
         assert_eq!(err.message(), Some("invalid stored block lengths"));
     }
+
+    fn compress_with_flush(flush: FlushCompress) -> Vec<u8> {
+        let incompressible = (0..=255).collect::<Vec<u8>>();
+        let mut output = vec![0; 1024];
+
+        // Feed in the incompressible data followed by the indicated flush type.
+        let mut w = Compress::new(Compression::default(), false);
+        w.compress(&incompressible, &mut output, flush).unwrap();
+
+        if flush != FlushCompress::None {
+            // The first instance of incompressible input should have been written uncompressed.
+            assert!(w.total_out() >= 261);
+            assert_eq!(&output[0..5], &[0, 0, 1, 0xff, !1]);
+            assert_eq!(&output[5..261], &incompressible);
+        }
+
+        // Feed in the same data again.
+        let len = w.total_out() as usize;
+        w.compress(&incompressible, &mut output[len..], FlushCompress::Finish)
+            .unwrap();
+
+        if flush != FlushCompress::Full {
+            // This time, the data should have been compressed (because it is an exact duplicate of
+            // the earlier block).
+            assert!(w.total_out() < 300);
+        }
+
+        // Assert that all input has been processed.
+        assert_eq!(w.total_in(), 256 * 2);
+
+        output.resize(w.total_out() as usize, 0);
+        output
+    }
+
+    #[test]
+    fn test_partial_flush() {
+        let output = compress_with_flush(FlushCompress::Partial);
+
+        // Check for partial flush marker.
+        assert_eq!(output[261], 0x2);
+        assert_eq!(output[262] & 0x7, 0x4);
+    }
+
+    #[test]
+    fn test_sync_flush() {
+        let output = compress_with_flush(FlushCompress::Sync);
+
+        // Check for sync flush marker.
+        assert_eq!(&output[261..][..5], &[0, 0, 0, 0xff, 0xff]);
+    }
+
+    #[test]
+    fn test_full_flush() {
+        let output = compress_with_flush(FlushCompress::Full);
+        assert_eq!(output.len(), 527);
+
+        // Check for flush flush marker.
+        assert_eq!(&output[261..][..5], &[0, 0, 0, 0xff, 0xff]);
+
+        // Check that the second instance of incompressible input was also written uncompressed.
+        assert_eq!(&output[266..][..5], &[1, 0, 1, 0xff, !1]);
+    }
 }