message: Improve test error message.
diff: @@ -78,8 +78,7 @@ first
  describe("cursor movements", () => {
  it("1-1", () => {
  - terminal.output.write(vttest("1-1"));
  - expect(terminal.output.toString()).to.contain(output(`
  + const expectedOutput = output(`
  ********************************************************************************
  *++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*
  *+ +*
  @@ -104,7 +103,20 @@ first
  *+ +*
  *++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*
  ********************************************************************************
  -`));
  +`);
  +
  + terminal.output.write(vttest("1-1"));
  + const actualOutput = terminal.output.toString();
  +
  + if (expectedOutput !== actualOutput) {
  + console.log("Expected output:");
  + console.log(expectedOutput);
  +
  + console.log("Actual output:");
  + console.log(actualOutput);
  +
  + expect(expectedOutput).to.eq(actualOutput);
  + }
  });
  });
  });
  