If it's suspected that there is a brain tumor, your doctor may recommend a number of tests and procedures, including:
A neurological exam
A neurological exam may include, among other things, checking the vision, hearing, balance, coordination, strength and reflexes. Difficulty in one or more areas may provide clues about the part of the brain that could be affected by a brain tumor.
Imaging tests
Magnetic resonance imaging (MRI) is commonly usdiagnose brain tumors. In some cases a dye may be injected through a vein in your arm during your MRI study. A number of specialized MRI scan components — including functional MRI, perfusion MRI and magnetic resonance spectroscopy — may help your doctor evaluate the tumor and plan treatment.
Other 
imaging tests may include computerized tomography (CT) scan and positron emission tomography (PET).
Tests to find cancer in other parts of your body
If it's suspected that the brain tumor may be a result of cancer that has spread from another area of the body, the doctor may recommend tests and procedures to determine where the cancer originated. One example might be a CT scan of the chest to look for signs of lung cancer.
Collecting and testing a sample of abnormal tissue (biopsy)
A biopsy can be performed as part of an operation to remove the brain tumor, or a biopsy can be performed using a needle. A stereotactic needle biopsy may be done for brain tumors in hard to reach areas or very sensitive areas within your brain that might be damaged by a more extensive operation. The neurosurgeon drills a small hole into your skull. A thin needle is then inserted through the hole. Tissue is removed using the needle, which is frequently guided by CT or MRI scanning. The biopsy sample is then viewed under a microscope to determine if it is cancerous or benign. This information is critical to establish a diagnosis and prognosis and, most importantly, in guiding treatment.