System.Tests.StringTests.LastIndexOf_AllSubstrings C# (CSharp) Method

        public static void LastIndexOf_AllSubstrings(string s, string value, int startIndex, StringComparison comparisonType)
        {
            bool ignoringCase = comparisonType == StringComparison.OrdinalIgnoreCase || comparisonType == StringComparison.CurrentCultureIgnoreCase;

            // First find the substring.  We should be able to with all comparison types.
            Assert.Equal(startIndex, s.LastIndexOf(value, comparisonType)); // in the whole string
            Assert.Equal(startIndex, s.LastIndexOf(value, startIndex + value.Length - 1, comparisonType)); // starting at end of substring
            Assert.Equal(startIndex, s.LastIndexOf(value, startIndex + value.Length, comparisonType)); // starting just beyond end of substring
            if (startIndex + value.Length < s.Length)
            {
                Assert.Equal(startIndex, s.LastIndexOf(value, startIndex + value.Length + 1, comparisonType)); // starting a bit more beyond end of substring
            }
            if (startIndex + value.Length > 1)
            {
                Assert.Equal(-1, s.LastIndexOf(value, startIndex + value.Length - 2, comparisonType)); // starting before end of substring
            }

            // Shouldn't be able to find the substring if the count is less than substring's length
            Assert.Equal(-1, s.LastIndexOf(value, s.Length - 1, value.Length - 1, comparisonType));

            // Now double the source.  Make sure we find the second copy of the substring.
            int halfLen = s.Length;
            s += s;
            Assert.Equal(halfLen + startIndex, s.LastIndexOf(value, comparisonType));

            // Now change the case of a letter.
            s = s.ToUpperInvariant();
            Assert.Equal(ignoringCase ? halfLen + startIndex : -1, s.LastIndexOf(value, comparisonType));
        }