Use TextDiffSubject to compare multi-line text (#406)

* Use TextDiffSubject to compare  multi-line text

It illustrates differences better.

Moved TextDiffSubject.java to the common project for sharing.

common/src/testing/java/google/registry/testing/truth/TextDiffSubject.java

@@ -0,0 +1,200 @@
+// Copyright 2019 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.testing.truth;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.truth.Truth.assertAbout;
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.github.difflib.DiffUtils;
+import com.github.difflib.UnifiedDiffUtils;
+import com.github.difflib.algorithm.DiffException;
+import com.github.difflib.patch.Patch;
+import com.github.difflib.text.DiffRow;
+import com.github.difflib.text.DiffRowGenerator;
+import com.google.common.base.Ascii;
+import com.google.common.base.Joiner;
+import com.google.common.base.Strings;
+import com.google.common.collect.ImmutableList;
+import com.google.common.io.Resources;
+import com.google.common.truth.Fact;
+import com.google.common.truth.FailureMetadata;
+import com.google.common.truth.Subject;
+import java.io.IOException;
+import java.net.URL;
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Compares two multi-line text blocks, and displays their diffs in readable formats.
+ *
+ * <p>User may choose one of the following diff formats:
+ *
+ * <ul>
+ *   <li>{@link DiffFormat#UNIFIED_DIFF} displays the differences in the unified-diff format
+ *   <li>{@link DiffFormat#SIDE_BY_SIDE_MARKDOWN} displays the two text blocks side by side, with
+ *       markdown annotations to highlight the differences.
+ * </ul>
+ *
+ * <p>Note that if one text block has one trailing newline at the end while another has none, this
+ * difference will not be shown in the generated diffs. This is the case where two texts may be
+ * reported as unequal but the diffs appear equal. Fixing this requires special treatment of the
+ * last line of text. The fix would not be useful in our environment, where all important files are
+ * covered by a style checker that ensures the presence of a trailing newline.
+ */
+// TODO(weiminyu): move this class and test to a standalone 'testing' project. Note that the util
+// project is not good since it depends back to core.
+public class TextDiffSubject extends Subject {
+
+  private final ImmutableList<String> actual;
+  private DiffFormat diffFormat = DiffFormat.SIDE_BY_SIDE_MARKDOWN;
+
+  protected TextDiffSubject(FailureMetadata metadata, List<String> actual) {
+    super(metadata, actual);
+    this.actual = ImmutableList.copyOf(actual);
+  }
+
+  public TextDiffSubject withDiffFormat(DiffFormat format) {
+    this.diffFormat = format;
+    return this;
+  }
+
+  public void hasSameContentAs(List<String> expectedContent) {
+    checkNotNull(expectedContent, "expectedContent");
+    ImmutableList<String> expected = ImmutableList.copyOf(expectedContent);
+    if (expected.equals(actual)) {
+      return;
+    }
+    String diffString = diffFormat.generateDiff(expected, actual);
+    failWithoutActual(
+        Fact.simpleFact(
+            Joiner.on('\n')
+                .join(
+                    "Files differ in content. Displaying " + Ascii.toLowerCase(diffFormat.name()),
+                    diffString)));
+  }
+
+  public void hasSameContentAs(URL resourceUrl) throws IOException {
+    hasSameContentAs(Resources.asCharSource(resourceUrl, UTF_8).readLines());
+  }
+
+  public static TextDiffSubject assertThat(List<String> actual) {
+    return assertAbout(textFactory()).that(ImmutableList.copyOf(checkNotNull(actual, "actual")));
+  }
+
+  public static TextDiffSubject assertThat(URL resourceUrl) throws IOException {
+    return assertThat(Resources.asCharSource(resourceUrl, UTF_8).readLines());
+  }
+
+  private static final Subject.Factory<TextDiffSubject, ImmutableList<String>>
+      TEXT_DIFF_SUBJECT_TEXT_FACTORY = TextDiffSubject::new;
+
+  public static Subject.Factory<TextDiffSubject, ImmutableList<String>> textFactory() {
+    return TEXT_DIFF_SUBJECT_TEXT_FACTORY;
+  }
+
+  static String generateUnifiedDiff(
+      ImmutableList<String> expectedContent, ImmutableList<String> actualContent) {
+    Patch<String> diff;
+    try {
+      diff = DiffUtils.diff(expectedContent, actualContent);
+    } catch (DiffException e) {
+      throw new RuntimeException(e);
+    }
+    List<String> unifiedDiff =
+        UnifiedDiffUtils.generateUnifiedDiff("expected", "actual", expectedContent, diff, 0);
+
+    return Joiner.on('\n').join(unifiedDiff);
+  }
+
+  static String generateSideBySideDiff(
+      ImmutableList<String> expectedContent, ImmutableList<String> actualContent) {
+    DiffRowGenerator generator =
+        DiffRowGenerator.create()
+            .showInlineDiffs(true)
+            .inlineDiffByWord(true)
+            .oldTag(f -> "~")
+            .newTag(f -> "**")
+            .build();
+    List<DiffRow> rows;
+    try {
+      rows = generator.generateDiffRows(expectedContent, actualContent);
+    } catch (DiffException e) {
+      throw new RuntimeException(e);
+    }
+
+    int maxExpectedLineLength =
+        findMaxLineLength(rows.stream().map(DiffRow::getOldLine).collect(Collectors.toList()));
+    int maxActualLineLength =
+        findMaxLineLength(rows.stream().map(DiffRow::getNewLine).collect(Collectors.toList()));
+
+    SideBySideRowFormatter sideBySideRowFormatter =
+        new SideBySideRowFormatter(maxExpectedLineLength, maxActualLineLength);
+
+    return Joiner.on('\n')
+        .join(
+            sideBySideRowFormatter.formatRow("Expected", "Actual", ' '),
+            sideBySideRowFormatter.formatRow("", "", '-'),
+            rows.stream()
+                .map(
+                    row ->
+                        sideBySideRowFormatter.formatRow(row.getOldLine(), row.getNewLine(), ' '))
+                .toArray());
+  }
+
+  private static int findMaxLineLength(Collection<String> lines) {
+    return lines.stream()
+        .max(Comparator.comparingInt(String::length))
+        .map(String::length)
+        .orElse(0);
+  }
+
+  private static class SideBySideRowFormatter {
+    private final int maxExpectedLineLength;
+    private final int maxActualLineLength;
+
+    private SideBySideRowFormatter(int maxExpectedLineLength, int maxActualLineLength) {
+      this.maxExpectedLineLength = maxExpectedLineLength;
+      this.maxActualLineLength = maxActualLineLength;
+    }
+
+    public String formatRow(String expected, String actual, char padChar) {
+      return String.format(
+          "|%s|%s|",
+          Strings.padEnd(expected, maxExpectedLineLength, padChar),
+          Strings.padEnd(actual, maxActualLineLength, padChar));
+    }
+  }
+
+  /** The format used to display diffs when two text blocks are different. */
+  public enum DiffFormat {
+    UNIFIED_DIFF {
+      @Override
+      String generateDiff(ImmutableList<String> expected, ImmutableList<String> actual) {
+        return generateUnifiedDiff(expected, actual);
+      }
+    },
+    SIDE_BY_SIDE_MARKDOWN {
+      @Override
+      String generateDiff(ImmutableList<String> expected, ImmutableList<String> actual) {
+        return generateSideBySideDiff(expected, actual);
+      }
+    };
+
+    abstract String generateDiff(ImmutableList<String> expected, ImmutableList<String> actual);
+  }
+}