[NFC] ASSERT_EQ before accessing items in containers

[kbobyrev]

Summary

As discussed offline, something different from EXPECT_EQ should be used to check if the container contains enough items before accessing them so that other tests can still be run even if the assertion fails as opposed to having EXPECT_EQ failing and then aborting the run due to the errors caused by out-of-bounds memory access.

[ilya-biryukov]

clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp

1877

We should not break out of the loop here.
Maybe do

if (size() != 1) {
  ADD_FAILURE() << "";
  continue;
}

[ilya-biryukov]

LGTM, but please update the other diff as well!

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

712

Same here, actually. We should not break out of the loop.

[ilya-biryukov]

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

713

add continue!

[kbobyrev]

Rebase on top of master.

clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp

constexpr const char *TestCodes[] = {
           Auxilary x;
           x.[[]]^;
         }
       )cpp"};
   for (const auto &Text : TestCodes) {
     Annotations TestCode(Text);
     auto Results = completions(Server, TestCode.code(), TestCode.point());
 
-    EXPECT_EQ(Results.Completions.size(), 1u);
+    ASSERT_EQ(Results.Completions.size(), 1u);
     EXPECT_THAT(Results.Completions.front().CompletionTokenRange,
                 TestCode.range());
   }
 }
 
 TEST(SignatureHelpTest, OverloadsOrdering) {
   const auto Results = signatures(R"cpp(
     void foo(int x);

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

void bar(X *x) {
   )cpp");
   auto TU = TestTU::withCode(Test.code());
   auto Index =
       buildIndexWithSymbol(SymbolWithHeader{"X", "unittest:///a.h", "\"a.h\""});
   TU.ExternalIndex = Index.get();
 
   auto Parsed = TU.build();
   for (const auto &D : Parsed.getDiagnostics()) {
-    EXPECT_EQ(D.Fixes.size(), 1u);
+    ASSERT_EQ(D.Fixes.size(), 1u);
     EXPECT_EQ(D.Fixes[0].Message,
               std::string("Add include \"a.h\" for symbol X"));
   }
 }
 
 TEST(IncludeFixerTest, UnresolvedNameAsSpecifier) {
   Annotations Test(R"cpp(
 $insert[[]]namespace ns {
 }